Crouch jumping

The crouch jump, also called "duck jump", or "High Jump", is a technique where one first jumps and then crouches in mid air. This will bring up your legs and, for some unknown reason, your entire body, allowing a little more height to reach higher places, such as better sniping positions. Also when you fall from heights that will give you death this trick maybe useful instead of death you get spared.

The method of crouch jumping is relatively simple. Press 'A' to jump and while in mid-air hold down crouch. This should enable you to get to previous unreachable places. The reason this trick works is not because it makes you jump higher. What actually happens is that when you do a normal jump, occasionally the place your trying to jump to too high and your feet hit the platform edge and you can't get to the place. When you crouch jump your feet get 'tucked into your body' so instead of hitting the platform edge, your feet land on the floor and you can now access higher platforms.

You can also while mid-air hit crouch repeatedly to gain more air time, but not necessarily more height. It also seems in Halo: CE that with a one handed weapon, (plasma pistol or pistol) you will look like your are jumping with no weapon to another player (arms apart).