2 players, but you can have round-robin tournaments! The players each extend their right hands (or left hands) and do the "sixties" style handshake where you make a "c" shape with your hands and lay your thumbs along the flat top of the fists. Then you slowly move the thumbs back and forth and say "1,2,3,4,we will have a thumb war;5,6,7,8, try to keep your thumb straight." Then, once the pleasantries are over the combatants try to pin down their opponent's thumb with their own while keeping their hands clasped. Great game for the car, waiting to be seated in a restaurant!
Contributed by Roberta Sanchez
This is a "cheat" kids nowadays play with thumb wrestling. It is called "Snake in the Grass."
Contributed by DarkMika - Thank you!