A martingale is a piece of equipment that keeps a horse from elavating  his head too high and to prevent a horse from avoiding a riders commands. It may also come in handy if you own a head tosser that could hit you in the face with his neck. Martingales are allowed in most classes that involve jumping or speed. However, are not allowed in flat most classes. There are standing martingales, running martingales, Germin martingales and a number of other devices used in training. It is not advisable for beginning riders to use these items unless they have had some schooling on there use.