From the official Yu-Gi-Oh Rule Book:
Players Duel each other using a variety of cards. You win a Duel if: 1. you reduce your opponent’s Life Points to 0; 2. if your opponent is unable to draw a card; or 3. if a card’s special effect says you win. If you both reach 0 Life Points at the same time, the Duel is a draw.
Updated November 17, 2012 to be compact and more user friendly. Subtotals seemed to be unnecessary since there is a running total but, as always, contact me if you have any comments or suggestions.