The present application discloses a helmet, a retention system for a helmet, and a method of adjusting a helmet. In certain embodiments, the helmet comprises a helmet shell and a retention system attached to the helmet shell. The retention system generally comprises a rear portion connected to the rear of the helmet shell, at least one strap extending from the rear portion to a front portion of the helmet shell, and an adjustment device attached to the rear portion and configured to selectively adjust the length of the strap between the rear portion and the front portion of the helmet shell.