diff --git a/lib/inspect/ip/address.ex b/lib/inspect/ip/address.ex
index 30a535b..f107af6 100644
--- a/lib/inspect/ip/address.ex
+++ b/lib/inspect/ip/address.ex
@@ -1,14 +1,15 @@
 defimpl Inspect, for: IP.Address do
+  alias IP.Address
+  import Inspect.Algebra
+
   @moduledoc """
   Implement the `Inspect` protocol for `IP.Address`
   """
-  alias IP.Address
-  import Inspect.Algebra
 
   @doc """
   Inpect an `address`.
 
-  # Examples
+  ## Examples
 
       iex> IP.Address.from_string!("192.0.2.1", 4)
       #IP.Address<192.0.2.1>
diff --git a/lib/inspect/ip/prefix.ex b/lib/inspect/ip/prefix.ex
new file mode 100644
index 0000000..20be0e6
--- /dev/null
+++ b/lib/inspect/ip/prefix.ex
@@ -0,0 +1,22 @@
+defimpl Inspect, for: IP.Prefix do
+  alias IP.Prefix
+  import Inspect.Algebra
+
+  @moduledoc """
+  Implement the `Inspect` protocol for `IP.Prefix`
+  """
+
+  @doc """
+  Inspect a `prefix`.
+
+  ## Examples
+
+      iex> IP.Address.from_string!("192.0.2.1", 4)
+      ...> |> IP.Address.to_prefix(32)
+      #IP.Prefix<192.0.2.1/32>
+  """
+  @spec inspect(Prefix.t, list) :: binary
+  def inspect(%Prefix{address: address, length: length}, _opts) do
+    concat ["#IP.Prefix<#{address}/#{length}>"]
+  end
+end
diff --git a/lib/ip/address.ex b/lib/ip/address.ex
index 1d8b968..de104ca 100644
--- a/lib/ip/address.ex
+++ b/lib/ip/address.ex
@@ -1,6 +1,6 @@
 defmodule IP.Address do
   alias __MODULE__
-  alias IP.Address.{InvalidAddress, V6, Helpers}
+  alias IP.Address.{InvalidAddress, Helpers, Prefix}
   defstruct ~w(address version)a
   import Helpers
   use Bitwise
@@ -106,6 +106,56 @@ defmodule IP.Address do
     end
   end
 
+  @doc """
+  Convert a string representation into an IP address of unknown version.
+
+  Tries to parse the string as IPv6, then IPv4 before failing.  Obviously if
+  you know the version then using `from_string/2` is faster.
+
+  ## Examples
+
+      iex> "192.0.2.1"
+      ...> |> IP.Address.from_string()
+      {:ok, %IP.Address{address: 3221225985, version: 4}}
+
+      iex> "2001:db8::1"
+      ...> |> IP.Address.from_string()
+      {:ok, %IP.Address{address: 42540766411282592856903984951653826561, version: 6}}
+  """
+  @spec from_string(binary) :: {:ok, t} | {:error, term}
+  def from_string(address) when is_binary(address) do
+    case from_string(address, 6) do
+      {:ok, address} -> {:ok, address}
+      {:error, _} ->
+        case from_string(address, 4) do
+          {:ok, address} -> {:ok, address}
+          {:error, _} -> {:error, "Unable to parse IP address"}
+        end
+    end
+  end
+
+  @doc """
+  Convert a string representation into an IP address or raise an
+  `IP.Address.InvalidAddress` exception.
+
+  ## Examples
+
+      iex> "192.0.2.1"
+      ...> |> IP.Address.from_string!()
+      %IP.Address{address: 3221225985, version: 4}
+
+      iex> "2001:db8::1"
+      ...> |> IP.Address.from_string!()
+      %IP.Address{address: 42540766411282592856903984951653826561, version: 6}
+  """
+  @spec from_string!(binary) :: t
+  def from_string!(address) when is_binary(address) do
+    case from_string(address) do
+      {:ok, addr} -> addr
+      {:error, msg} -> raise(InvalidAddress, message: msg)
+    end
+  end
+
   @doc """
   Convert a string representation into an IP address of specified version.
 
@@ -121,18 +171,25 @@ defmodule IP.Address do
   """
   @spec from_string(binary, ip_version) :: {:ok, t} | {:error, term}
   def from_string(address, 4) when is_binary(address) do
-    address = address
-      |> String.split(".")
-      |> Enum.map(&String.to_integer(&1))
-      |> from_bytes()
-
-    {:ok, %Address{version: 4, address: address}}
+    case :inet.parse_ipv4_address(String.to_charlist(address)) do
+      {:ok, addr} ->
+        addr = addr
+          |> Tuple.to_list()
+          |> from_bytes()
+        {:ok, %Address{version: 4, address: addr}}
+      {:error, _} -> {:error, "Cannot parse IPv4 address"}
+    end
   end
 
   def from_string(address, 6) when is_binary(address) do
-    address = address
-      |> V6.to_integer()
-      {:ok, %Address{version: 6, address: address}}
+    case :inet.parse_ipv6strict_address(String.to_charlist(address)) do
+      {:ok, addr} ->
+        addr = addr
+          |> Tuple.to_list()
+          |> from_bytes()
+        {:ok, %Address{version: 6, address: addr}}
+      {:error, _} -> {:error, "Cannot parse IPv6 address"}
+    end
   end
 
   def from_string(_address, 4), do: {:error, "Cannot parse IPv4 address"}
@@ -140,7 +197,7 @@ defmodule IP.Address do
   def from_string(_address, version), do: {:error, "No such IP version #{inspect version}"}
 
   @doc """
-  Convert a string representation into an IP address of specified versionor raise an
+  Convert a string representation into an IP address of specified version or raise an
   `IP.Address.InvalidAddress` exception.
 
   ## Examples
@@ -180,7 +237,9 @@ defmodule IP.Address do
     b = addr >>> 0x10 &&& 0xff
     c = addr >>> 0x08 &&& 0xff
     d = addr &&& 0xff
-    "#{a}.#{b}.#{c}.#{d}"
+    {a, b, c, d}
+    |> :inet.ntoa()
+    |> List.to_string()
   end
 
   def to_string(%Address{version: 6, address: addr}) do
@@ -192,13 +251,29 @@ defmodule IP.Address do
     f = addr >>> 0x20 &&& 0xffff
     g = addr >>> 0x10 &&& 0xffff
     h = addr &&& 0xffff
-    [a, b, c, d, e, f, g, h]
-    |> Enum.map(&Integer.to_string(&1, 16))
-    |> Enum.join(":")
-    |> V6.compress()
+    {a, b, c, d, e, f, g, h}
+    |> :inet.ntoa()
+    |> List.to_string()
   end
 
+  @doc """
+  Convert an `address` to an `IP.Prefix`.
+
+  ## Examples
+
+      iex> IP.Address.from_string!("192.0.2.1", 4)
+      ...> |> IP.Address.to_prefix(32)
+      #IP.Prefix<192.0.2.1/32>
+  """
+  @spec to_prefix(t, Prefix.ipv4_prefix_length | Prefix.ipv6_prefix_length) :: Prefix.t
+  def to_prefix(%Address{} = address, length), do: IP.Prefix.new(address, length)
+
   defp from_bytes([a, b, c, d]) do
     (a <<< 24) + (b <<< 16) + (c <<< 8) + d
   end
+
+  defp from_bytes([a, b, c, d, e, f, g, h]) do
+    (a <<< 0x70) + (b <<< 0x60) + (c <<< 0x50) + (d <<< 0x40) +
+    (e <<< 0x30) + (f <<< 0x20) + (g <<< 0x10) + h
+  end
 end
diff --git a/lib/ip/address/v6.ex b/lib/ip/address/v6.ex
deleted file mode 100644
index 74c8f73..0000000
--- a/lib/ip/address/v6.ex
+++ /dev/null
@@ -1,109 +0,0 @@
-defmodule IP.Address.V6 do
-  use Bitwise
-
-  @moduledoc """
-  Helper module for working with IPv6 address strings.
-  """
-
-  @doc """
-  Expand a compressed address.
-
-  ## Examples
-
-      iex> "2001:db8::1"
-      ...> |> IP.Address.V6.expand()
-      "2001:0db8:0000:0000:0000:0000:0000:0001"
-
-      iex> "2001:0db8:0000:0000:0000:0000:0000:0001"
-      ...> |> IP.Address.V6.expand()
-      "2001:0db8:0000:0000:0000:0000:0000:0001"
-  """
-  @spec expand(binary) :: {:ok, binary} | {:error, term}
-  def expand(address) do
-    address
-    |> expand_to_ints()
-    |> Enum.map(fn (i) ->
-      i
-      |> Integer.to_string(16)
-      |> String.pad_leading(4, "0")
-    end)
-    |> Enum.join(":")
-    |> String.downcase()
-  end
-
-  @doc """
-  Compress an IPv6 address
-
-  ## Examples
-
-      iex> "2001:0db8:0000:0000:0000:0000:0000:0001"
-      ...> |> IP.Address.V6.compress()
-      "2001:db8::1"
-
-      iex> "2001:db8::1"
-      ...> |> IP.Address.V6.compress()
-      "2001:db8::1"
-  """
-  @spec compress(binary) :: binary
-  def compress(address) do
-    address = address
-      |> expand_to_ints()
-      |> Enum.map(&Integer.to_string(&1, 16))
-      |> Enum.join(":")
-      |> String.downcase()
-    Regex.replace(~r/\b(?:0+:){2,}/, address, ":")
-  end
-
-  @doc """
-  Convert an IPv6 into a 128 bit integer
-
-  ## Examples
-
-      iex> "2001:0db8:0000:0000:0000:0000:0000:0001"
-      ...> |> IP.Address.V6.to_integer()
-      42540766411282592856903984951653826561
-
-      iex> "2001:db8::1"
-      ...> |> IP.Address.V6.to_integer()
-      42540766411282592856903984951653826561
-  """
-  @spec to_integer(binary) :: non_neg_integer
-  def to_integer(address) do
-    address
-    |> expand_to_ints()
-    |> reduce_ints(0)
-  end
-
-  defp reduce_ints([], addr), do: addr
-  defp reduce_ints([next | remaining] = all, addr) do
-    left_shift_size = (length(all) - 1) * 16
-    addr = addr + (next <<< left_shift_size)
-    reduce_ints(remaining, addr)
-  end
-
-  defp expand_to_ints(address) do
-    case String.split(address, "::") do
-      [head, tail] ->
-        head = decolonify(head)
-        tail = decolonify(tail)
-        pad(head, tail)
-      [head] -> decolonify(head)
-    end
-  end
-
-  defp decolonify(chunk) do
-    chunk
-    |> String.split(":")
-    |> Enum.map(&String.to_integer(&1, 16))
-  end
-
-  defp pad(head, []) when length(head) == 8, do: head
-  defp pad([], tail) when length(tail) == 8, do: tail
-  defp pad(head, tail) when length(head) + length(tail) < 8 do
-    head_len = length(head)
-    tail_len = length(head)
-    pad_len  = 8 - (head_len + tail_len)
-    pad      = Enum.map(0..pad_len, fn (_) -> 0 end)
-    head ++ pad ++ tail
-  end
-end
diff --git a/lib/ip/prefix.ex b/lib/ip/prefix.ex
new file mode 100644
index 0000000..a986f18
--- /dev/null
+++ b/lib/ip/prefix.ex
@@ -0,0 +1,32 @@
+defmodule IP.Prefix do
+  alias IP.{Prefix, Address}
+  defstruct ~w(address length)a
+
+  @moduledoc """
+  Defines an IP prefix, otherwise known as a subnet.
+  """
+
+  @type t :: %Prefix{}
+  @type ipv4_prefix_length :: 0..32
+  @type ipv6_prefix_length :: 0..128
+
+  @doc """
+  Create an IP prefix from an `IP.Address` and `length`.
+
+  ## Examples
+
+      iex> IP.Prefix.new(IP.Address.from_string!("192.0.2.1", 4), 32)
+      %IP.Prefix{address: %IP.Address{address: 3221225985, version: 4}, length: 32}
+
+      iex> IP.Prefix.new(IP.Address.from_string!("2001:db8::1", 6), 128)
+      %IP.Prefix{address: %IP.Address{address: 42540766411282592856903984951653826561, version: 6}, length: 128}
+  """
+  @spec new(Address.t, ipv4_prefix_length | ipv6_prefix_length) :: t
+  def new(%Address{version: 4} = address, length) when length > 0 and length <= 32 do
+    %Prefix{address: address, length: length}
+  end
+
+  def new(%Address{version: 6} = address, length) when length > 0 and length <= 128 do
+    %Prefix{address: address, length: length}
+  end
+end
diff --git a/lib/string/chars/ip/address.ex b/lib/string/chars/ip/address.ex
index 3536e1a..03bad24 100644
--- a/lib/string/chars/ip/address.ex
+++ b/lib/string/chars/ip/address.ex
@@ -6,7 +6,7 @@ defimpl String.Chars, for: IP.Address do
   @doc ~S"""
   Convert an `address` into a string representation.
 
-  # Examples
+  ## Examples
 
       iex> "#{IP.Address.from_string!("192.0.2.1", 4)}"
       "192.0.2.1"
diff --git a/lib/string/chars/ip/prefix.ex b/lib/string/chars/ip/prefix.ex
new file mode 100644
index 0000000..30e898b
--- /dev/null
+++ b/lib/string/chars/ip/prefix.ex
@@ -0,0 +1,20 @@
+defimpl String.Chars, for: IP.Prefix do
+  alias IP.Prefix
+  @moduledoc """
+  Implements `String.Chars` for `IP.Prefix`.
+  """
+
+  @doc ~S"""
+  Convert a `prefix` into a string representation.
+
+  ## Examples
+
+      iex> address = IP.Address.from_string!("192.0.2.1", 4)
+      ...> prefix = IP.Prefix.new(address, 32)
+      ...> "#{prefix}"
+      "192.0.2.1/32"
+  """
+  def to_string(%Prefix{address: address, length: length}) do
+    "#{address}/#{length}"
+  end
+end
diff --git a/test/ip/address/v6_test.exs b/test/ip/address/v6_test.exs
deleted file mode 100644
index d88f8c4..0000000
--- a/test/ip/address/v6_test.exs
+++ /dev/null
@@ -1,4 +0,0 @@
-defmodule IPAddressV6Test do
-  use ExUnit.Case
-  doctest IP.Address.V6
-end
diff --git a/test/ip/prefix_test.exs b/test/ip/prefix_test.exs
new file mode 100644
index 0000000..14f0fd0
--- /dev/null
+++ b/test/ip/prefix_test.exs
@@ -0,0 +1,4 @@
+defmodule IPPrefixTest do
+  use ExUnit.Case
+  doctest IP.Prefix
+end
diff --git a/test/string/chars/ip/prefix_test.exs b/test/string/chars/ip/prefix_test.exs
new file mode 100644
index 0000000..e7508bc
--- /dev/null
+++ b/test/string/chars/ip/prefix_test.exs
@@ -0,0 +1,4 @@
+defmodule StringCharsIPPrefixTest do
+  use ExUnit.Case
+  doctest String.Chars.IP.Prefix
+end