How many doubles grand slam titles have the William sisters won?

As of August 2012, Serena Williams has won 14 major Singles titles. She has won the Australian Open 5 times (2003, 2005, 2007, 2009, 2010), Wimbledon 5 times (2002, 2003, 2009, 2010, 2012), the US Open 3 times (1999, 2002, 2008) and the French Open once (2002).

She has also won 13 Ladies' Doubles major titles; with these coming 5 times at Wimbledon (2000, 2002, 2008, 2009, 2012), 4 times at the Australian Open (2001, 2003, 2009, 2010), 2 times at the French Open (1999, 2010) and also twice at the US Open (1999, 2009). All of these victories came alongside her sister, Venus.

She has also won 2 Mixed Doubles major titles, with these both coming in 1998 at Wimbledon and the US Open.