diff --git a/shared/src/main/scala/com/comcast/ip4s/Host.scala b/shared/src/main/scala/com/comcast/ip4s/Host.scala
index 2045fc5..e0680fa 100644
--- a/shared/src/main/scala/com/comcast/ip4s/Host.scala
+++ b/shared/src/main/scala/com/comcast/ip4s/Host.scala
@@ -215,6 +215,9 @@ sealed abstract class IpAddress extends IpAddressPlatform with Host with Seriali
   def asSourceSpecificMulticastLenient: Option[SourceSpecificMulticast[this.type]] =
     SourceSpecificMulticast.fromIpAddressLenient(this)
 
+  /** Returns true if this address is in a private range. */
+  def isPrivate: Boolean
+
   /** Narrows this address to an Ipv4Address if that is the underlying type. */
   def asIpv4: Option[Ipv4Address] = collapseMappedV4.fold(Some(_), _ => None)
 
@@ -356,6 +359,11 @@ final class Ipv4Address private (protected val bytes: Array[Byte]) extends IpAdd
   override def isSourceSpecificMulticast: Boolean =
     this >= Ipv4Address.SourceSpecificMulticastRangeStart && this <= Ipv4Address.SourceSpecificMulticastRangeEnd
 
+  override def isPrivate: Boolean =
+    Ipv4Address.Classes.Private.A.contains(this) ||
+      Ipv4Address.Classes.Private.B.contains(this) ||
+      Ipv4Address.Classes.Private.C.contains(this)
+
   /** Converts this V4 address to a compat V6 address, where the first 12 bytes are all zero and the last 4 bytes
     * contain the bytes of this V4 address.
     */
@@ -418,6 +426,38 @@ object Ipv4Address extends Ipv4AddressCompanionPlatform {
   val SourceSpecificMulticastRangeEnd: Ipv4Address =
     fromBytes(232, 255, 255, 255)
 
+  /** IPv4 address classes represented as CIDRs. */
+  object Classes {
+
+    /** Class A: 0.0.0.0 - 127.255.255.255 */
+    val A: Cidr[Ipv4Address] = Cidr(fromBytes(0, 0, 0, 0), 1)
+
+    /** Class B: 128.0.0.0 - 191.255.255.255 */
+    val B: Cidr[Ipv4Address] = Cidr(fromBytes(128, 0, 0, 0), 2)
+
+    /** Class C: 192.0.0.0 - 223.255.255.255 */
+    val C: Cidr[Ipv4Address] = Cidr(fromBytes(192, 0, 0, 0), 3)
+
+    /** Class D: 224.0.0.0 - 239.255.255.255 */
+    val D: Cidr[Ipv4Address] = Cidr(fromBytes(224, 0, 0, 0), 4)
+
+    /** Class E: 240.0.0.0 - 255.255.255.255 */
+    val E: Cidr[Ipv4Address] = Cidr(fromBytes(240, 0, 0, 0), 5)
+
+    /** Private address ranges. */
+    object Private {
+
+      /** Class A: 10.0.0.0 - 10.255.255.255 */
+      val A: Cidr[Ipv4Address] = Cidr(fromBytes(10, 0, 0, 0), 8)
+
+      /** Class B: 172.16.0.0 - 172.31.255.255 */
+      val B: Cidr[Ipv4Address] = Cidr(fromBytes(172, 16, 0, 0), 12)
+
+      /** Class A: 192.168.0.0 - 192.168.255.255 */
+      val C: Cidr[Ipv4Address] = Cidr(fromBytes(192, 168, 0, 0), 16)
+    }
+  }
+
   /** Parses an IPv4 address from a dotted-decimal string, returning `None` if the string is not a valid IPv4 address.
     */
   def fromString(value: String): Option[Ipv4Address] = {
@@ -609,6 +649,9 @@ final class Ipv6Address private (protected val bytes: Array[Byte]) extends IpAdd
   override def isSourceSpecificMulticast: Boolean =
     this >= Ipv6Address.SourceSpecificMulticastRangeStart && this <= Ipv6Address.SourceSpecificMulticastRangeEnd
 
+  override def isPrivate: Boolean =
+    Ipv6Address.UniqueLocalBlock.contains(this) || (isMappedV4 && collapseMappedV4.isPrivate)
+
   /** Applies the supplied mask to this address.
     *
     * @example {{{
@@ -653,6 +696,10 @@ object Ipv6Address extends Ipv6AddressCompanionPlatform {
   val MappedV4Block: Cidr[Ipv6Address] =
     Cidr(Ipv6Address.fromBytes(0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 255, 255, 0, 0, 0, 0), 96)
 
+  /** CIDR which defines unique local address block. */
+  val UniqueLocalBlock: Cidr[Ipv6Address] =
+    Cidr(Ipv6Address.fromBytes(0xfc, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0), 7)
+
   /** Parses an IPv6 address from a string in RFC4291 notation, returning `None` if the string is not a valid IPv6
     * address.
     */
diff --git a/test-kit/shared/src/test/scala/com/comcast/ip4s/Ipv4AddressTest.scala b/test-kit/shared/src/test/scala/com/comcast/ip4s/Ipv4AddressTest.scala
index a955cd6..a190ff8 100644
--- a/test-kit/shared/src/test/scala/com/comcast/ip4s/Ipv4AddressTest.scala
+++ b/test-kit/shared/src/test/scala/com/comcast/ip4s/Ipv4AddressTest.scala
@@ -67,4 +67,21 @@ class Ipv4AddressTest extends BaseTestSuite {
     assertEquals(Ipv4Address.fromString("0.0.0.0").map(_.previous), Ipv4Address.fromString("255.255.255.255"))
     forAll { (ip: Ipv4Address) => assertEquals(ip.previous, Ipv4Address.fromLong(ip.toLong - 1)) }
   }
+
+  test("isPrivate") {
+    assert(!ipv4"10.0.0.0".previous.isPrivate)
+    assert(ipv4"10.0.0.0".isPrivate)
+    assert(ipv4"10.255.255.255".isPrivate)
+    assert(!ipv4"10.255.255.255".next.isPrivate)
+
+    assert(!ipv4"172.16.0.0".previous.isPrivate)
+    assert(ipv4"172.16.0.0".isPrivate)
+    assert(ipv4"172.31.255.255".isPrivate)
+    assert(!ipv4"172.31.255.255".next.isPrivate)
+
+    assert(!ipv4"192.168.0.0".previous.isPrivate)
+    assert(ipv4"192.168.0.0".isPrivate)
+    assert(ipv4"192.168.255.255".isPrivate)
+    assert(!ipv4"192.168.255.255".next.isPrivate)
+  }
 }
diff --git a/test-kit/shared/src/test/scala/com/comcast/ip4s/Ipv6AddressTest.scala b/test-kit/shared/src/test/scala/com/comcast/ip4s/Ipv6AddressTest.scala
index 4cab33c..4d845f7 100644
--- a/test-kit/shared/src/test/scala/com/comcast/ip4s/Ipv6AddressTest.scala
+++ b/test-kit/shared/src/test/scala/com/comcast/ip4s/Ipv6AddressTest.scala
@@ -131,4 +131,13 @@ class Ipv6AddressTest extends BaseTestSuite {
     assertEquals[Any, Any](addr.asIpv6, Some(addr))
     assertEquals[Any, Any](addr.asIpv4, Some(ip"0.15.0.15"))
   }
+
+  test("isPrivate") {
+    assert(!ipv6"fc00::".previous.isPrivate)
+    assert(ipv6"fc00::".isPrivate)
+    assert(ipv6"fe00::".previous.isPrivate)
+    assert(!ipv6"fe00::".isPrivate)
+    // mapped v4
+    assert(ipv6"::ffff:10.1.1.1".isPrivate)
+  }
 }