diff --git a/okio/src/commonMain/kotlin/okio/-Base64.kt b/okio/src/commonMain/kotlin/okio/-Base64.kt
index bdf2e1bc65..9d401ce3f3 100644
--- a/okio/src/commonMain/kotlin/okio/-Base64.kt
+++ b/okio/src/commonMain/kotlin/okio/-Base64.kt
@@ -18,36 +18,32 @@
 @file:JvmName("-Base64")
 package okio
 
-import okio.ByteString.Companion.encodeUtf8
 import kotlin.jvm.JvmName
 
 /** @author Alexander Y. Kleymenov */
 
-internal val BASE64 =
-    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/".encodeUtf8().data
-internal val BASE64_URL_SAFE =
-    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_".encodeUtf8().data
+internal const val BASE64 =
+    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
+internal const val BASE64_URL_SAFE =
+    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_"
 
-internal fun String.decodeBase64ToArray(): ByteArray? {
+fun Buffer.commonWriteBase64(string: String): Buffer {
   // Ignore trailing '=' padding and whitespace from the input.
-  var limit = length
+  var limit = string.length
   while (limit > 0) {
-    val c = this[limit - 1]
+    val c = string[limit - 1]
     if (c != '=' && c != '\n' && c != '\r' && c != ' ' && c != '\t') {
       break
     }
     limit--
   }
 
-  // If the input includes whitespace, this output array will be longer than necessary.
-  val out = ByteArray((limit * 6L / 8L).toInt())
-  var outCount = 0
   var inCount = 0
-
   var word = 0
-  for (pos in 0 until limit) {
-    val c = this[pos]
-
+  var pos = 0
+  var s = head
+  while (pos < limit) {
+    val c = string[pos++]
     val bits: Int
     if (c in 'A'..'Z') {
       // char ASCII value
@@ -71,7 +67,7 @@ internal fun String.decodeBase64ToArray(): ByteArray? {
     } else if (c == '\n' || c == '\r' || c == ' ' || c == '\t') {
       continue
     } else {
-      return null
+      throw IllegalArgumentException("Invalid Base64") // TODO: Dedicated exception? IOException?
     }
 
     // Append this char's 6 bits to the word.
@@ -80,9 +76,17 @@ internal fun String.decodeBase64ToArray(): ByteArray? {
     // For every 4 chars of input, we accumulate 24 bits of output. Emit 3 bytes.
     inCount++
     if (inCount % 4 == 0) {
-      out[outCount++] = (word shr 16).toByte()
-      out[outCount++] = (word shr 8).toByte()
-      out[outCount++] = word.toByte()
+      if (s == null || s.limit + 3 > Segment.SIZE) {
+        // For simplicity, don't try to write blocks across different segments, allocate new segment when current doesn't have enough capacity
+        s = writableSegment(3)
+      }
+      val data = s.data
+      var i = s.limit
+      data[i++] = (word shr 16).toByte()
+      data[i++] = (word shr 8).toByte()
+      data[i++] = word.toByte()
+      s.limit = i
+      size += 3
     }
   }
 
@@ -90,59 +94,96 @@ internal fun String.decodeBase64ToArray(): ByteArray? {
   when (lastWordChars) {
     1 -> {
       // We read 1 char followed by "===". But 6 bits is a truncated byte! Fail.
-      return null
+      throw IllegalArgumentException("Invalid Base64") // TODO: Dedicated exception? IOException?
     }
     2 -> {
       // We read 2 chars followed by "==". Emit 1 byte with 8 of those 12 bits.
+      if (s == null || s.limit + 1 > Segment.SIZE) {
+        s = writableSegment(1)
+      }
       word = word shl 12
-      out[outCount++] = (word shr 16).toByte()
+      s.data[s.limit++] = (word shr 16).toByte()
+      size += 1
     }
     3 -> {
       // We read 3 chars, followed by "=". Emit 2 bytes for 16 of those 18 bits.
+      if (s == null || s.limit + 2 > Segment.SIZE) {
+        s = writableSegment(2)
+      }
       word = word shl 6
-      out[outCount++] = (word shr 16).toByte()
-      out[outCount++] = (word shr 8).toByte()
+      val data = s.data
+      var i = s.limit
+      data[i++] = (word shr 16).toByte()
+      data[i++] = (word shr 8).toByte()
+      s.limit = i
+      size += 2
     }
   }
 
-  // If we sized our out array perfectly, we're done.
-  if (outCount == out.size) return out
-
-  // Copy the decoded bytes to a new, right-sized array.
-  return out.copyOf(outCount)
+  return this
 }
 
-internal fun ByteArray.encodeBase64(map: ByteArray = BASE64): String {
-  val length = (size + 2) / 3 * 4
-  val out = ByteArray(length)
+fun Buffer.commonReadBase64(): String =
+  readBase64(BASE64)
+
+fun Buffer.commonReadBase64Url(): String =
+  readBase64(BASE64_URL_SAFE)
+
+private fun Buffer.readBase64(map: String = BASE64): String {
+  val length = ((size + 2) / 3 * 4).toInt() // TODO: Prevent Int overflow / arithmetic overflow ?
+  val out = CharArray(length)
   var index = 0
-  val end = size - size % 3
-  var i = 0
-  while (i < end) {
-    val b0 = this[i++].toInt()
-    val b1 = this[i++].toInt()
-    val b2 = this[i++].toInt()
-    out[index++] = map[(b0 and 0xff shr 2)]
-    out[index++] = map[(b0 and 0x03 shl 4) or (b1 and 0xff shr 4)]
-    out[index++] = map[(b1 and 0x0f shl 2) or (b2 and 0xff shr 6)]
-    out[index++] = map[(b2 and 0x3f)]
+  while (size >= 3) {
+    val s = head!!
+    val segmentSize = s.limit - s.pos
+    if (segmentSize > 3) {
+      // Read all complete blocks from head segment
+      val data = s.data
+      val end = s.limit - segmentSize % 3
+      var i = s.pos
+      while (i < end) {
+        val b0 = data[i++].toInt()
+        val b1 = data[i++].toInt()
+        val b2 = data[i++].toInt()
+        out[index++] = map[(b0 and 0xff shr 2)]
+        out[index++] = map[(b0 and 0x03 shl 4) or (b1 and 0xff shr 4)]
+        out[index++] = map[(b1 and 0x0f shl 2) or (b2 and 0xff shr 6)]
+        out[index++] = map[(b2 and 0x3f)]
+      }
+      size -= end - s.pos
+      if (end == s.limit) {
+        head = s.pop()
+        SegmentPool.recycle(s)
+      } else {
+        s.pos = end
+      }
+    } else {
+      // Read next block, which is spread over multiple segments
+      val b0 = readByte().toInt()
+      val b1 = readByte().toInt()
+      val b2 = readByte().toInt()
+      out[index++] = map[(b0 and 0xff shr 2)]
+      out[index++] = map[(b0 and 0x03 shl 4) or (b1 and 0xff shr 4)]
+      out[index++] = map[(b1 and 0x0f shl 2) or (b2 and 0xff shr 6)]
+      out[index++] = map[(b2 and 0x3f)]
+    }
   }
-  when (size - end) {
-    1 -> {
-      val b0 = this[i].toInt()
+  when (size) {
+    1L -> {
+      val b0 = readByte().toInt()
       out[index++] = map[b0 and 0xff shr 2]
       out[index++] = map[b0 and 0x03 shl 4]
-      out[index++] = '='.toByte()
-      out[index] = '='.toByte()
+      out[index++] = '='
+      out[index] = '='
     }
-    2 -> {
-      val b0 = this[i++].toInt()
-      val b1 = this[i].toInt()
+    2L -> {
+      val b0 = readByte().toInt()
+      val b1 = readByte().toInt()
       out[index++] = map[(b0 and 0xff shr 2)]
       out[index++] = map[(b0 and 0x03 shl 4) or (b1 and 0xff shr 4)]
       out[index++] = map[(b1 and 0x0f shl 2)]
-      out[index] = '='.toByte()
+      out[index] = '='
     }
   }
-  return out.toUtf8String()
+  return out.concatToString()
 }
diff --git a/okio/src/commonMain/kotlin/okio/Buffer.kt b/okio/src/commonMain/kotlin/okio/Buffer.kt
index 1ff7342556..0bbc7abb07 100644
--- a/okio/src/commonMain/kotlin/okio/Buffer.kt
+++ b/okio/src/commonMain/kotlin/okio/Buffer.kt
@@ -114,6 +114,8 @@ expect class Buffer() : BufferedSource, BufferedSink {
 
   override fun writeHexadecimalUnsignedLong(v: Long): Buffer
 
+  override fun writeBase64(string: String): Buffer
+
   /** Returns a deep copy of this buffer.  */
   fun copy(): Buffer
 
diff --git a/okio/src/commonMain/kotlin/okio/BufferedSink.kt b/okio/src/commonMain/kotlin/okio/BufferedSink.kt
index 40c26585c8..0646ae49b9 100644
--- a/okio/src/commonMain/kotlin/okio/BufferedSink.kt
+++ b/okio/src/commonMain/kotlin/okio/BufferedSink.kt
@@ -241,6 +241,11 @@ expect interface BufferedSink : Sink {
    */
   fun writeHexadecimalUnsignedLong(v: Long): BufferedSink
 
+  /**
+   * Decodes the Base64-encoded bytes from [string] and writes them to this sink.
+   */
+  fun writeBase64(string: String): BufferedSink
+
   /**
    * Writes all buffered data to the underlying sink, if one exists. Then that sink is recursively
    * flushed which pushes data as far as possible towards its ultimate destination. Typically that
diff --git a/okio/src/commonMain/kotlin/okio/BufferedSource.kt b/okio/src/commonMain/kotlin/okio/BufferedSource.kt
index 0ba4d152bd..eccda298c0 100644
--- a/okio/src/commonMain/kotlin/okio/BufferedSource.kt
+++ b/okio/src/commonMain/kotlin/okio/BufferedSource.kt
@@ -421,6 +421,18 @@ expect interface BufferedSource : Source {
    */
   fun readUtf8CodePoint(): Int
 
+  /**
+   * Removes all bytes from this, encodes them as as [Base64](http://www.ietf.org/rfc/rfc2045.txt), and returns the
+   * string. In violation of the RFC, the returned string does not wrap lines at 76 columns.
+   */
+  fun readBase64(): String
+
+  /**
+   * Removes all bytes from this, encodes them as as [URL-safe Base64](http://www.ietf.org/rfc/rfc4648.txt), and
+   * returns the string.
+   */
+  fun readBase64Url(): String
+
   /** Equivalent to [indexOf(b, 0)][indexOf]. */
   fun indexOf(b: Byte): Long
 
diff --git a/okio/src/commonMain/kotlin/okio/internal/ByteString.kt b/okio/src/commonMain/kotlin/okio/internal/ByteString.kt
index 5f0ec021e4..1d4fe82ded 100644
--- a/okio/src/commonMain/kotlin/okio/internal/ByteString.kt
+++ b/okio/src/commonMain/kotlin/okio/internal/ByteString.kt
@@ -16,7 +16,6 @@
 
 package okio.internal
 
-import okio.BASE64_URL_SAFE
 import okio.Buffer
 import okio.ByteString
 import okio.REPLACEMENT_CODE_POINT
@@ -24,10 +23,9 @@ import okio.and
 import okio.arrayRangeEquals
 import okio.asUtf8ToByteArray
 import okio.checkOffsetAndCount
-import okio.decodeBase64ToArray
-import okio.encodeBase64
 import okio.isIsoControl
 import okio.processUtf8CodePoints
+import okio.commonReadBase64Url
 import okio.shr
 import okio.toUtf8String
 
@@ -46,10 +44,12 @@ internal inline fun ByteString.commonUtf8(): String {
 }
 
 @Suppress("NOTHING_TO_INLINE")
-internal inline fun ByteString.commonBase64(): String = data.encodeBase64()
+internal inline fun ByteString.commonBase64(): String =
+  Buffer().write(this).readBase64()
 
 @Suppress("NOTHING_TO_INLINE")
-internal inline fun ByteString.commonBase64Url() = data.encodeBase64(map = BASE64_URL_SAFE)
+internal inline fun ByteString.commonBase64Url(): String =
+  Buffer().write(this).commonReadBase64Url()
 
 internal val HEX_DIGIT_CHARS =
   charArrayOf('0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f')
@@ -266,8 +266,13 @@ internal inline fun String.commonEncodeUtf8(): ByteString {
 
 @Suppress("NOTHING_TO_INLINE")
 internal inline fun String.commonDecodeBase64(): ByteString? {
-  val decoded = decodeBase64ToArray()
-  return if (decoded != null) ByteString(decoded) else null
+  val buffer = Buffer()
+  try {
+    buffer.writeBase64(this)
+  } catch (e: IllegalArgumentException) { // TODO: Dedicated Base64 exception?
+    return null
+  }
+  return buffer.readByteString()
 }
 
 @Suppress("NOTHING_TO_INLINE")
diff --git a/okio/src/commonMain/kotlin/okio/internal/RealBufferedSink.kt b/okio/src/commonMain/kotlin/okio/internal/RealBufferedSink.kt
index 49b0c4d755..54aae6bd6b 100644
--- a/okio/src/commonMain/kotlin/okio/internal/RealBufferedSink.kt
+++ b/okio/src/commonMain/kotlin/okio/internal/RealBufferedSink.kt
@@ -163,6 +163,12 @@ internal inline fun RealBufferedSink.commonWriteHexadecimalUnsignedLong(v: Long)
   return emitCompleteSegments()
 }
 
+internal inline fun RealBufferedSink.commonWriteBase64(string: String): BufferedSink {
+  check(!closed) { "closed" }
+  buffer.writeBase64(string)
+  return emitCompleteSegments()
+}
+
 internal inline fun RealBufferedSink.commonEmitCompleteSegments(): BufferedSink {
   check(!closed) { "closed" }
   val byteCount = buffer.completeSegmentByteCount()
diff --git a/okio/src/commonMain/kotlin/okio/internal/RealBufferedSource.kt b/okio/src/commonMain/kotlin/okio/internal/RealBufferedSource.kt
index 40938ea2f8..b955058449 100644
--- a/okio/src/commonMain/kotlin/okio/internal/RealBufferedSource.kt
+++ b/okio/src/commonMain/kotlin/okio/internal/RealBufferedSource.kt
@@ -110,6 +110,16 @@ internal inline fun RealBufferedSource.commonReadByteArray(byteCount: Long): Byt
   return buffer.readByteArray(byteCount)
 }
 
+internal inline fun RealBufferedSource.commonReadBase64(): String {
+  buffer.writeAll(source)
+  return buffer.readBase64()
+}
+
+internal inline fun RealBufferedSource.commonReadBase64Url(): String {
+  buffer.writeAll(source)
+  return buffer.readBase64Url()
+}
+
 internal inline fun RealBufferedSource.commonReadFully(sink: ByteArray) {
   try {
     require(sink.size.toLong())
diff --git a/okio/src/jsMain/kotlin/okio/Buffer.kt b/okio/src/jsMain/kotlin/okio/Buffer.kt
index 402bf6c41d..28a742ea49 100644
--- a/okio/src/jsMain/kotlin/okio/Buffer.kt
+++ b/okio/src/jsMain/kotlin/okio/Buffer.kt
@@ -130,6 +130,10 @@ actual class Buffer : BufferedSource, BufferedSink {
 
   override fun readUtf8CodePoint(): Int = commonReadUtf8CodePoint()
 
+  override fun readBase64(): String = commonReadBase64()
+
+  override fun readBase64Url(): String = commonReadBase64Url()
+
   override fun select(options: Options): Int = commonSelect(options)
 
   override fun readByteArray(): ByteArray = commonReadByteArray()
@@ -192,6 +196,9 @@ actual class Buffer : BufferedSource, BufferedSink {
   actual override fun writeHexadecimalUnsignedLong(v: Long): Buffer =
     commonWriteHexadecimalUnsignedLong(v)
 
+  actual override fun writeBase64(string: String): Buffer =
+    commonWriteBase64(string)
+
   override fun write(source: Buffer, byteCount: Long): Unit = commonWrite(source, byteCount)
 
   override fun read(sink: Buffer, byteCount: Long): Long = commonRead(sink, byteCount)
diff --git a/okio/src/jsMain/kotlin/okio/BufferedSink.kt b/okio/src/jsMain/kotlin/okio/BufferedSink.kt
index 65d717c60a..20db6cbc00 100644
--- a/okio/src/jsMain/kotlin/okio/BufferedSink.kt
+++ b/okio/src/jsMain/kotlin/okio/BufferedSink.kt
@@ -54,6 +54,8 @@ actual interface BufferedSink : Sink {
 
   actual fun writeHexadecimalUnsignedLong(v: Long): BufferedSink
 
+  actual fun writeBase64(string: String): BufferedSink
+
   actual fun emit(): BufferedSink
 
   actual fun emitCompleteSegments(): BufferedSink
diff --git a/okio/src/jsMain/kotlin/okio/BufferedSource.kt b/okio/src/jsMain/kotlin/okio/BufferedSource.kt
index 98b7718a14..23323e81e6 100644
--- a/okio/src/jsMain/kotlin/okio/BufferedSource.kt
+++ b/okio/src/jsMain/kotlin/okio/BufferedSource.kt
@@ -76,6 +76,10 @@ actual interface BufferedSource : Source {
 
   actual fun readUtf8CodePoint(): Int
 
+  actual fun readBase64(): String
+
+  actual fun readBase64Url(): String
+
   actual fun indexOf(b: Byte): Long
 
   actual fun indexOf(b: Byte, fromIndex: Long): Long
diff --git a/okio/src/jsMain/kotlin/okio/RealBufferedSink.kt b/okio/src/jsMain/kotlin/okio/RealBufferedSink.kt
index ed03094ec3..924fe32316 100644
--- a/okio/src/jsMain/kotlin/okio/RealBufferedSink.kt
+++ b/okio/src/jsMain/kotlin/okio/RealBufferedSink.kt
@@ -24,6 +24,7 @@ import okio.internal.commonTimeout
 import okio.internal.commonToString
 import okio.internal.commonWrite
 import okio.internal.commonWriteAll
+import okio.internal.commonWriteBase64
 import okio.internal.commonWriteByte
 import okio.internal.commonWriteDecimalLong
 import okio.internal.commonWriteHexadecimalUnsignedLong
@@ -66,6 +67,7 @@ internal actual class RealBufferedSink actual constructor(
   override fun writeLongLe(v: Long) = commonWriteLongLe(v)
   override fun writeDecimalLong(v: Long) = commonWriteDecimalLong(v)
   override fun writeHexadecimalUnsignedLong(v: Long) = commonWriteHexadecimalUnsignedLong(v)
+  override fun writeBase64(string: String): BufferedSink = commonWriteBase64(string)
   override fun emitCompleteSegments() = commonEmitCompleteSegments()
   override fun emit() = commonEmit()
   override fun flush() = commonFlush()
diff --git a/okio/src/jsMain/kotlin/okio/RealBufferedSource.kt b/okio/src/jsMain/kotlin/okio/RealBufferedSource.kt
index d6f4b94221..bec6bd7b87 100644
--- a/okio/src/jsMain/kotlin/okio/RealBufferedSource.kt
+++ b/okio/src/jsMain/kotlin/okio/RealBufferedSource.kt
@@ -23,6 +23,8 @@ import okio.internal.commonPeek
 import okio.internal.commonRangeEquals
 import okio.internal.commonRead
 import okio.internal.commonReadAll
+import okio.internal.commonReadBase64
+import okio.internal.commonReadBase64Url
 import okio.internal.commonReadByte
 import okio.internal.commonReadByteArray
 import okio.internal.commonReadByteString
@@ -62,6 +64,8 @@ internal actual class RealBufferedSource actual constructor(
   override fun select(options: Options): Int = commonSelect(options)
   override fun readByteArray(): ByteArray = commonReadByteArray()
   override fun readByteArray(byteCount: Long): ByteArray = commonReadByteArray(byteCount)
+  override fun readBase64(): String = commonReadBase64()
+  override fun readBase64Url(): String = commonReadBase64Url()
   override fun read(sink: ByteArray): Int = read(sink, 0, sink.size)
   override fun readFully(sink: ByteArray): Unit = commonReadFully(sink)
   override fun read(sink: ByteArray, offset: Int, byteCount: Int): Int =
diff --git a/okio/src/jvmMain/kotlin/okio/Buffer.kt b/okio/src/jvmMain/kotlin/okio/Buffer.kt
index c514bb6eba..9c76b01bb3 100644
--- a/okio/src/jvmMain/kotlin/okio/Buffer.kt
+++ b/okio/src/jvmMain/kotlin/okio/Buffer.kt
@@ -330,6 +330,12 @@ actual class Buffer : BufferedSource, BufferedSink, Cloneable, ByteChannel {
   @Throws(EOFException::class)
   override fun readUtf8CodePoint(): Int = commonReadUtf8CodePoint()
 
+  @Throws(EOFException::class)
+  override fun readBase64(): String = commonReadBase64()
+
+  @Throws(EOFException::class)
+  override fun readBase64Url(): String = commonReadBase64Url()
+
   override fun readByteArray() = commonReadByteArray()
 
   @Throws(EOFException::class)
@@ -448,6 +454,9 @@ actual class Buffer : BufferedSource, BufferedSink, Cloneable, ByteChannel {
   actual override fun writeHexadecimalUnsignedLong(v: Long): Buffer =
     commonWriteHexadecimalUnsignedLong(v)
 
+  actual override fun writeBase64(string: String): Buffer =
+    commonWriteBase64(string)
+
   internal actual fun writableSegment(minimumCapacity: Int): Segment =
     commonWritableSegment(minimumCapacity)
 
diff --git a/okio/src/jvmMain/kotlin/okio/BufferedSink.kt b/okio/src/jvmMain/kotlin/okio/BufferedSink.kt
index edb632f910..953293ae2b 100644
--- a/okio/src/jvmMain/kotlin/okio/BufferedSink.kt
+++ b/okio/src/jvmMain/kotlin/okio/BufferedSink.kt
@@ -90,6 +90,9 @@ actual interface BufferedSink : Sink, WritableByteChannel {
   @Throws(IOException::class)
   actual fun writeHexadecimalUnsignedLong(v: Long): BufferedSink
 
+  @Throws(IOException::class)
+  actual fun writeBase64(string: String): BufferedSink
+
   @Throws(IOException::class)
   actual override fun flush()
 
diff --git a/okio/src/jvmMain/kotlin/okio/BufferedSource.kt b/okio/src/jvmMain/kotlin/okio/BufferedSource.kt
index b30c635ae2..24d328f2a1 100644
--- a/okio/src/jvmMain/kotlin/okio/BufferedSource.kt
+++ b/okio/src/jvmMain/kotlin/okio/BufferedSource.kt
@@ -117,6 +117,12 @@ actual interface BufferedSource : Source, ReadableByteChannel {
   @Throws(IOException::class)
   actual fun readUtf8CodePoint(): Int
 
+  @Throws(IOException::class)
+  actual fun readBase64(): String
+
+  @Throws(IOException::class)
+  actual fun readBase64Url(): String
+
   /** Removes all bytes from this, decodes them as `charset`, and returns the string. */
   @Throws(IOException::class)
   fun readString(charset: Charset): String
diff --git a/okio/src/jvmMain/kotlin/okio/RealBufferedSink.kt b/okio/src/jvmMain/kotlin/okio/RealBufferedSink.kt
index 7df3f93776..d3fb3ec5ef 100644
--- a/okio/src/jvmMain/kotlin/okio/RealBufferedSink.kt
+++ b/okio/src/jvmMain/kotlin/okio/RealBufferedSink.kt
@@ -23,6 +23,7 @@ import okio.internal.commonTimeout
 import okio.internal.commonToString
 import okio.internal.commonWrite
 import okio.internal.commonWriteAll
+import okio.internal.commonWriteBase64
 import okio.internal.commonWriteByte
 import okio.internal.commonWriteDecimalLong
 import okio.internal.commonWriteHexadecimalUnsignedLong
@@ -100,6 +101,7 @@ internal actual class RealBufferedSink actual constructor(
   override fun writeLongLe(v: Long) = commonWriteLongLe(v)
   override fun writeDecimalLong(v: Long) = commonWriteDecimalLong(v)
   override fun writeHexadecimalUnsignedLong(v: Long) = commonWriteHexadecimalUnsignedLong(v)
+  override fun writeBase64(string: String): BufferedSink = commonWriteBase64(string)
   override fun emitCompleteSegments() = commonEmitCompleteSegments()
   override fun emit() = commonEmit()
 
diff --git a/okio/src/jvmMain/kotlin/okio/RealBufferedSource.kt b/okio/src/jvmMain/kotlin/okio/RealBufferedSource.kt
index 109ef1402e..1a58f9e288 100644
--- a/okio/src/jvmMain/kotlin/okio/RealBufferedSource.kt
+++ b/okio/src/jvmMain/kotlin/okio/RealBufferedSource.kt
@@ -23,6 +23,8 @@ import okio.internal.commonPeek
 import okio.internal.commonRangeEquals
 import okio.internal.commonRead
 import okio.internal.commonReadAll
+import okio.internal.commonReadBase64
+import okio.internal.commonReadBase64Url
 import okio.internal.commonReadByte
 import okio.internal.commonReadByteArray
 import okio.internal.commonReadByteString
@@ -72,6 +74,8 @@ internal actual class RealBufferedSource actual constructor(
   override fun select(options: Options): Int = commonSelect(options)
   override fun readByteArray(): ByteArray = commonReadByteArray()
   override fun readByteArray(byteCount: Long): ByteArray = commonReadByteArray(byteCount)
+  override fun readBase64(): String = commonReadBase64()
+  override fun readBase64Url(): String = commonReadBase64Url()
   override fun read(sink: ByteArray): Int = read(sink, 0, sink.size)
   override fun readFully(sink: ByteArray): Unit = commonReadFully(sink)
   override fun read(sink: ByteArray, offset: Int, byteCount: Int): Int =
diff --git a/okio/src/jvmTest/kotlin/okio/BufferBase64Test.kt b/okio/src/jvmTest/kotlin/okio/BufferBase64Test.kt
new file mode 100644
index 0000000000..73df64b147
--- /dev/null
+++ b/okio/src/jvmTest/kotlin/okio/BufferBase64Test.kt
@@ -0,0 +1,135 @@
+package okio
+
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.junit.runners.Parameterized
+import java.util.*
+import kotlin.test.assertEquals
+import kotlin.test.assertFailsWith
+
+@RunWith(Parameterized::class)
+class BufferBase64Test(val size: Int) {
+
+  private val random = Random(4975347L + size)
+  private val bytes = random.nextBytes(size)
+
+  companion object {
+    @get:Parameterized.Parameters(name = "{0}")
+    @get:JvmStatic
+    val parameters: List<Int>
+      get() = (0..32).toList() + ((Segment.SIZE - 32)..Segment.SIZE + 32).toList()
+
+    private val base64Encoder = Base64.getEncoder()
+    private val base64UrlEncoder = Base64.getUrlEncoder()
+
+    private fun Random.nextBytes(size: Int): ByteArray =
+      ByteArray(size).also { nextBytes(it) }
+  }
+
+  @Test
+  fun write() {
+    val encoded = base64Encoder.encodeToString(bytes)
+
+    val buffer = Buffer().apply { writeBase64(encoded) }
+
+    val byteArray = buffer.readByteArray()
+    assertArrayEquals(bytes, byteArray)
+  }
+
+  @Test
+  fun writeWithWhitespace() {
+    val encoded = base64Encoder.encodeToString(bytes).chunked(8).joinToString("\n")
+
+    val buffer = Buffer().apply { writeBase64(encoded) }
+
+    val byteArray = buffer.readByteArray()
+    assertArrayEquals(bytes, byteArray)
+  }
+
+  @Test
+  fun writeCorruptedInvalidChar() {
+    if (size == 0) return // Skip this test when there is no data
+    val corruptedIndex = random.nextInt(size)
+    val encoded =
+      base64Encoder.encodeToString(bytes).replaceRange(corruptedIndex..corruptedIndex, "?")
+
+    val buffer = Buffer()
+    assertFailsWith<IllegalArgumentException> {
+      buffer.writeBase64(encoded)
+    }
+  }
+
+  @Test
+  fun writeCorruptedInvalidLength() {
+    if (size == 0) return // Skip this test when there is no data
+    val encoded = base64Encoder.encodeToString(bytes) + "A"
+
+    val buffer = Buffer()
+    assertFailsWith<IllegalArgumentException> {
+      buffer.writeBase64(encoded)
+    }
+  }
+
+  @Test
+  fun writeMultiple() {
+    val buffer = Buffer().apply {
+      bytes.asList().chunked(4).forEach {
+        val encoded = base64Encoder.encodeToString(it.toByteArray())
+        writeBase64(encoded)
+      }
+    }
+
+    val byteArray = buffer.readByteArray()
+    assertArrayEquals(bytes, byteArray)
+  }
+
+  @Test
+  fun writeUrlEncoded() {
+    val encoded = base64UrlEncoder.encodeToString(bytes)
+
+    val buffer = Buffer().apply { writeBase64(encoded) }
+
+    val byteArray = buffer.readByteArray()
+    assertArrayEquals(bytes, byteArray)
+  }
+
+  @Test
+  fun read() {
+    val buffer = Buffer().apply { write(bytes) }
+
+    val s = buffer.readBase64()
+
+    assertEquals(base64Encoder.encodeToString(bytes), s)
+  }
+
+  @Test
+  fun readUrlEncoded() {
+    val buffer = Buffer().apply { write(bytes) }
+
+    val s = buffer.readBase64Url()
+
+    val encoded = base64UrlEncoder.encodeToString(bytes)
+    assertEquals(encoded, s)
+  }
+
+  @Test
+  fun readFragmented() {
+    // Buffer made of segments with only one byte, randomly located
+    val buffer = Buffer().apply {
+      bytes.forEach {
+        val s = writableSegment(Segment.SIZE)
+        check(s.pos == 0 && s.limit == 0) // Implementation should provide an empty segment
+        val pos = random.nextInt(Segment.SIZE)
+        s.pos = pos
+        s.data[pos] = it
+        s.limit = pos + 1
+        size++
+      }
+    }
+
+    val s = buffer.readBase64()
+
+    val encoded = base64Encoder.encodeToString(bytes)
+    assertEquals(encoded, s)
+  }
+}
diff --git a/okio/src/nativeMain/kotlin/okio/Buffer.kt b/okio/src/nativeMain/kotlin/okio/Buffer.kt
index 49623cbae8..63be873dc7 100644
--- a/okio/src/nativeMain/kotlin/okio/Buffer.kt
+++ b/okio/src/nativeMain/kotlin/okio/Buffer.kt
@@ -132,6 +132,10 @@ actual class Buffer : BufferedSource, BufferedSink {
 
   override fun readUtf8CodePoint(): Int = commonReadUtf8CodePoint()
 
+  override fun readBase64(): String = commonReadBase64()
+
+  override fun readBase64Url(): String = commonReadBase64Url()
+
   override fun readByteArray(): ByteArray = commonReadByteArray()
 
   override fun readByteArray(byteCount: Long): ByteArray = commonReadByteArray(byteCount)
@@ -192,6 +196,9 @@ actual class Buffer : BufferedSource, BufferedSink {
   actual override fun writeHexadecimalUnsignedLong(v: Long): Buffer =
     commonWriteHexadecimalUnsignedLong(v)
 
+  actual override fun writeBase64(string: String): Buffer =
+    commonWriteBase64(string)
+
   override fun write(source: Buffer, byteCount: Long): Unit = commonWrite(source, byteCount)
 
   override fun read(sink: Buffer, byteCount: Long): Long = commonRead(sink, byteCount)
diff --git a/okio/src/nativeMain/kotlin/okio/BufferedSink.kt b/okio/src/nativeMain/kotlin/okio/BufferedSink.kt
index 65d717c60a..20db6cbc00 100644
--- a/okio/src/nativeMain/kotlin/okio/BufferedSink.kt
+++ b/okio/src/nativeMain/kotlin/okio/BufferedSink.kt
@@ -54,6 +54,8 @@ actual interface BufferedSink : Sink {
 
   actual fun writeHexadecimalUnsignedLong(v: Long): BufferedSink
 
+  actual fun writeBase64(string: String): BufferedSink
+
   actual fun emit(): BufferedSink
 
   actual fun emitCompleteSegments(): BufferedSink
diff --git a/okio/src/nativeMain/kotlin/okio/BufferedSource.kt b/okio/src/nativeMain/kotlin/okio/BufferedSource.kt
index 98b7718a14..23323e81e6 100644
--- a/okio/src/nativeMain/kotlin/okio/BufferedSource.kt
+++ b/okio/src/nativeMain/kotlin/okio/BufferedSource.kt
@@ -76,6 +76,10 @@ actual interface BufferedSource : Source {
 
   actual fun readUtf8CodePoint(): Int
 
+  actual fun readBase64(): String
+
+  actual fun readBase64Url(): String
+
   actual fun indexOf(b: Byte): Long
 
   actual fun indexOf(b: Byte, fromIndex: Long): Long
diff --git a/okio/src/nativeMain/kotlin/okio/RealBufferedSink.kt b/okio/src/nativeMain/kotlin/okio/RealBufferedSink.kt
index ed03094ec3..924fe32316 100644
--- a/okio/src/nativeMain/kotlin/okio/RealBufferedSink.kt
+++ b/okio/src/nativeMain/kotlin/okio/RealBufferedSink.kt
@@ -24,6 +24,7 @@ import okio.internal.commonTimeout
 import okio.internal.commonToString
 import okio.internal.commonWrite
 import okio.internal.commonWriteAll
+import okio.internal.commonWriteBase64
 import okio.internal.commonWriteByte
 import okio.internal.commonWriteDecimalLong
 import okio.internal.commonWriteHexadecimalUnsignedLong
@@ -66,6 +67,7 @@ internal actual class RealBufferedSink actual constructor(
   override fun writeLongLe(v: Long) = commonWriteLongLe(v)
   override fun writeDecimalLong(v: Long) = commonWriteDecimalLong(v)
   override fun writeHexadecimalUnsignedLong(v: Long) = commonWriteHexadecimalUnsignedLong(v)
+  override fun writeBase64(string: String): BufferedSink = commonWriteBase64(string)
   override fun emitCompleteSegments() = commonEmitCompleteSegments()
   override fun emit() = commonEmit()
   override fun flush() = commonFlush()
diff --git a/okio/src/nativeMain/kotlin/okio/RealBufferedSource.kt b/okio/src/nativeMain/kotlin/okio/RealBufferedSource.kt
index d6f4b94221..bec6bd7b87 100644
--- a/okio/src/nativeMain/kotlin/okio/RealBufferedSource.kt
+++ b/okio/src/nativeMain/kotlin/okio/RealBufferedSource.kt
@@ -23,6 +23,8 @@ import okio.internal.commonPeek
 import okio.internal.commonRangeEquals
 import okio.internal.commonRead
 import okio.internal.commonReadAll
+import okio.internal.commonReadBase64
+import okio.internal.commonReadBase64Url
 import okio.internal.commonReadByte
 import okio.internal.commonReadByteArray
 import okio.internal.commonReadByteString
@@ -62,6 +64,8 @@ internal actual class RealBufferedSource actual constructor(
   override fun select(options: Options): Int = commonSelect(options)
   override fun readByteArray(): ByteArray = commonReadByteArray()
   override fun readByteArray(byteCount: Long): ByteArray = commonReadByteArray(byteCount)
+  override fun readBase64(): String = commonReadBase64()
+  override fun readBase64Url(): String = commonReadBase64Url()
   override fun read(sink: ByteArray): Int = read(sink, 0, sink.size)
   override fun readFully(sink: ByteArray): Unit = commonReadFully(sink)
   override fun read(sink: ByteArray, offset: Int, byteCount: Int): Int =