Bill -- One difference is that von Neumann/Nash games typically assume a payoff (a reward or loss) to participants upon termination of the game, whereas the abstract games discussed in game semantics usually do not assume this. Players in the latter either just win or lose, or the game is drawn, at termination; there is no other reward to the players. Accordingly, the games of game semantics are closer in spirit and design to the dialogue games studied and played by philosophers since at least the time of Aristotle, and which now form the basis for design of computer interaction protocols. Presumably the reseach funding agencies who sponsored Aristotle's research will be pleased that it is, at long last, being exploited commercially! Best, -- Peter McBurney University of Liverpool