Capture the Flag
Capture the flag in Halo 3 has the same basic rules as the real-life kids game it draws inspiration from. Grab your opponent's flag and bring it back to your base to earn a point. There are several modifications of this game type, such as first team to three flags or offense versus defense.
Territories
In a territories match, large sections of the battlefield are highlighted. Stand in that zone for a set amount of time to capture the territory. After capturing the zone, your team starts earning time. Earn the most time before the game ends to win.
Slayer
Slayer is a typical first-person shooter deathmatch-style game type. Be the first team or player to reach the set kill count--usually 50 for a team or 25 for free-for-all--to win.
Oddball
This objective-based match begins with a skull placed in the center of the level. Grab the skull to earn points based on time of possession. The caveat is the skull-holder cannot fire his weapons and walks slowly.
Assault
Grab a bomb and stealthily march it toward the opposing team's base. Stand in the team's highlighted bomb zone to arm the bomb. Afterward, the opposing team has a few seconds to disarm the bomb before it explodes. If you successfully defend the armed bomb, and it explodes, your team earns a point. If the other team disarms the bomb, they have a chance to arm it in your base to earn a point.