diff --git a/lib/ipaddr.rb b/lib/ipaddr.rb
index b0df4d3..c840ccb 100644
--- a/lib/ipaddr.rb
+++ b/lib/ipaddr.rb
@@ -195,6 +195,19 @@ def include?(other)
   end
   alias === include?
 
+  def private?
+    # RFC1918: Private Address Space
+    @@__private_network_class_a ||= self.class.new("10.0.0.0/8")
+    @@__private_network_class_b ||= self.class.new("172.16.0.0/12")
+    @@__private_network_class_c ||= self.class.new("192.168.0.0/16")
+
+    return true if @@__private_network_class_a.include?(self) || \
+                   @@__private_network_class_b.include?(self) || \
+                   @@__private_network_class_c.include?(self)
+
+    return false
+  end
+
   # Returns the integer representation of the ipaddr.
   def to_i
     return @addr
diff --git a/test/test_ipaddr.rb b/test/test_ipaddr.rb
index 88b4a01..8a0ec15 100644
--- a/test/test_ipaddr.rb
+++ b/test/test_ipaddr.rb
@@ -243,6 +243,21 @@ def test_include?
 
   end
 
+  def test_private?
+    assert_equal(true, IPAddr.new("10.0.0.0").private?)
+    assert_equal(true, IPAddr.new("10.255.255.255").private?)
+
+    assert_equal(true, IPAddr.new("172.16.0.0").private?)
+    assert_equal(true, IPAddr.new("172.31.255.255").private?)
+
+    assert_equal(true, IPAddr.new("192.168.0.0").private?)
+    assert_equal(true, IPAddr.new("192.168.255.255").private?)
+
+    assert_equal(false, IPAddr.new("192.1.0.0").private?)
+    assert_equal(false, IPAddr.new("172.32.0.0").private?)
+    assert_equal(false, IPAddr.new("11.0.0.0").private?)
+  end
+
   def test_hash
     a1 = IPAddr.new('192.168.2.0')
     a2 = IPAddr.new('192.168.2.0')