Abstract: An automatically operable window sash lock having a gravity-biased latch plate locking element. The latch plate is biased to a locking position wherein the latch plate is engaged with a catch. The latch structure may be mounted on one window member and the catch may be mounted on an adjacent window member. The latch structure is arranged to cause the latch plate to move to the locked position automatically as the result of the window members being moved to a closed position. The latch structure is further arranged to be retained in a retracted position when it is desired to move the window members to an open position.