Close grip pull up is one of the basic variations of the basic pull up. Putting your hands closer togather helps to activate your biceps more then in regular variations. Combining this exercise with underhand grip is proven to maximize the pressure on your biceps muscles (close grip chin up).

Preparation:
Grab the bar with your hands full extended. Hands should be around 6 inches apart from each other (close grip). Bar can be held with overhand, underhand or narrow grip.

Execution:
Begin the exercise by bending the elbows and pulling yourself up until your chin is over the bar. Hold this position for a second and slowly lower your body back to dead hang.

Muscles involved:
Back (lats), biceps, shoulders (posterior part), forearms.

Remember not to kip or swing to gain momentum while doing the exercise. Try to eliminate this as soon as possible, as it may turn into a habbit and will be hard to unlearn. Don't drop your body rapidly after your chin is over the bar because this may lead to injuries. Also, try to engage your abdominal muscles during the exercise. This exercise can be performed with a variety of grips, for example: overhand, underhand, neutral, mixed etc. Exercise should be performed on a bar or gymnastic rings. Exhale as you pull your body up and inhale when you lower yourself back.
This exercise is proven to be easier than wide grip pull up as it puts more pressure on your biceps and less pressure on your lats and posterior deltoid. In close grip pull ups, you have a longer range of motion than in wide grip pull ups and standard pull ups, which allows your lats to stretch deeper while in dead hang (starting position).