Essentially a variation on the much older game of whist, which led to bridge and auction bridge, the modern game of contract bridge resulted from rule refinements set down by Harold Stirling Vanderbilt in 1925. It is a card game played between four people divided into two teams. Play consists in a bidding phase followed by a phase in which the hands are played in an attempt to win "tricks". The height of its popularity, both as a pastime and competitively, was between the 1930s and the 1960s.