A sequential game is one during which players build choices (or choose a strategy) following an exact predefined order, and during which a minimum of some players will observe the moves of players who preceded them. If no players observe the moves of previous players, then the sport is simultaneous. If each player observes the moves of each different player who has gone before her, the sport is one among excellent data. If some (but not all) players observe previous moves, whereas others move simultaneously, the sport is one among imperfect data. Sequential games are represented by game trees (the in depth form) and solved using the concept of rollback, or subgame excellent equilibrium.