A dive knife is an important tool for cutting entanglements you may encounter underwater. These include fishing line, nets, rope, and kelp. Contrary to what you may have seen in movies, they are not used for self-defense against marine life.

A variety of blade styles are available for different purposes. Knives with pointed tips are popular for spearfishing, while a blunt tip is popular for prying objects loose. Your dive shop will be able to help you select the best knife for your needs.

Your knife should be carried in a quick-release sheath mounted in an accessible location. This can be the inside of your lower leg, outside of your BC, or for some models, your BC's low-pressure inflator hose.

Some knives have a metal end or tank banger on the handle. This is tapped against your tank to gain your buddy's attention.