From a competitors point of view, the contest rules are fairly simple. Which is how we will be examining the rules here. For a complete list of the Judo contest rules please see:
Judo Practice Uniform - Judo Gi
The original Judo gi was shorter in the sleeves and pant legs, more closely matching the traditional Japanese Kimono of the day. As Japan adopted more of the customs of the West, and as Judo spread throughout the world, the sleeve and pant length was increased to match that of a business suit. Today the gi sleeves should fall comfortably to your wrists and the pants should hang to the tops of your feet. Since you are providing the equipment for you partner to grip, and your partner is providing the equipment for you to grip, there should be sufficient slack in the gi throughout the arms for your partner to take a grip. The material should be sturdy enough to stand up to being pulled on, but supple enough to be gripped. Your gi should be clean and in good repair. Your belt should be properly and securely tied around your waste, and should represent the color of the official Judo rank you hold.
Contest Area - Shiai Jo
The contest area consists of a safety zone, which the players should generally avoid, and the main contest area. If you and your partner enter the safety zone as the result of attacking action, the referee will allow the action to continue as long as it is safe for you and your partner. Forcing your partner into the safety zone, or entering the safety zone without attacking action will result in a penalty.
Bowing - Rie
When entering the contest area, you will bow out of the world as you enter the safety zone. You will then formally bow into the competition area as you exit the safety zone. As you and your partner approach each other toward the center of the mat, you will bow to each other as a show of respect and take one step forward. This lets the referee know you are ready to being the contest.