The object of the game is to score the most points by rolling five dice to make certain combinations to get the most points. Each player uses three rolls per turn to try and get the combination they desire. they are 13 turn per player per game. The game is called Yahtzee because it is the highest point value combination in the game. Yahtzee is when a player get all five dice to be the same number in three rolls or less.
http://www.skooldays.com/categories/toys/ty1154.htm
http://curiosity.discovery.com/question/who-invented-yahtzee
http://en.wikipedia.org/wiki/Yahtzee