When using the buddy system, two or more SCUBA divers dive together and co-operate with each other, so that they can help or rescue each other in the event of an emergency.

It is a safety procedure that improves the divers' chances of avoiding or surviving accidents in or underwater. A pair of divers is the best combination in buddy diving: with threesomes, one of the divers can easily lose the attention of the other two. The system is likely to be effective in mitigating out-of-air emergencies, non-diving medical emergencies and entrapment in ropes or nets. When used with the buddy check it can help avoid equipment omission, misuse and failure.

With buddy diving each of the divers is presumed to have a responsibility to the other. The "buddies" are expected to monitor each other, to stay close enough together to be able to help in an emergency, to behave safely and to follow the plan agreed by the pair before the dive. When the system fails, it is generally because one of the divers does not live up to his or her responsibilities as a buddy.

Alternatives

The two alternatives, solo diving and diving as an individual in a large group, have disadvantages when compared to the buddy system especially for the novice.

• Although solo diving is used by some divers in technical diving, it is only effective if the diver is totally self-sufficient. This is not possible in some cases, such as entrappment in ropes and nets and in non-diving medical emergencies.
• In group diving, especially in large groups, poor visibility or currents, individual divers can easily become detached from the group and lose the protection of any experienced divers in the group.

Other uses

• A similar system of pairs is used during firefighting, where it is called the two-in, two-out principle.

• The buddy system has also been widely adapted for use in public school field trips. The teacher will pair the students into groups of two as a safety precaution and to hopefully avoid mischief.

• In computing, buddy system is often used as a synonym for buddy memory allocation.

• In American teenage street lingo, the buddy system refers to code phrase of asking the question Hey you got any bud? to strangers connotating cannabis, but denotating Budweiser beer when questioned by authority figures.

• For participants in NaNoEdMo, buddy system refers to the mandatory practice of staying in touch with a partner who can give advice or help with editing if needed, and testify that 50 hours of work have been done.