Freediving is a technique used with various aquatic activities. While in general all aquatic activities that include breath-hold diving might be classified as a part of freediving, some sports are more accepted than others. 

Competitive freediving is currently governed by two world associations: AIDA International (International Association for Development of Apnea) and CMAS (World Underwater Federation). Most types of competitive freediving have in common that it is an individual sport based on the best individual achievement. An exception to this rule is the bi-annual World Championship for Teams, held by AIDA, where the combined score of the team members makes up the team's total points. There are currently nine disciplines used by official governing bodies and a dozen disciplines that are only practiced locally. In this article, the recognized disciplines of AIDA and CMAS will be described. All disciplines can be done by both men and women and, while done outdoors, no differences in the environment between records are recognized any longer. The disciplines of AIDA can be done both in competition and as a record attempt, with the exception of Variable Weight and No limits, which are both done solely as record attempts.

Training for freediving can take many forms and be done on the land.

One example is the apnea walk. This consists of a preparation "breathe-up", followed by a short (typically 1 minute) breath hold taken at rest. Without breaking the hold, the participant then initiates a walk for as far as they can, until it becomes necessary to breathe again. Athletes can do close to 400 meters in training this way.

This form of training is good for accustoming muscles to work under anaerobic conditions, and for tolerance to CO₂ build-up in the circulation. It is also easy to gauge progress, as increasing distance can be measured.

Before diving, performance-oriented freedivers hyperventilate to a certain degree, resulting in a lower level of CO₂ in their lungs and bloodstream.

This postpones the start of stimulation to the breathing centre of the brain, and thus delays the warning signals of running out of air. As the oxygen level of the blood is not increased by hyperventilation, this is very dangerous and may contribute to shallow water blackout and deep water blackout.

Trained freedivers are well aware of this and will only dive under strict and first aid competent supervision. However this does not, of itself, eliminate the risk of deep or shallow water blackout. All safe freedivers have a 'buddy' who accompanies them, observing from within the water at the surface. Due to the nature of the sport, safety is an integral part of free-diving, requiring participants to be adept in rescue and resuscitation. Without proper training and supervision, free-diving/apnea/breath-hold diving is extremely dangerous.

Archaeologists said that people have been earning their sustenance from freediving since the 5th century BCE. The first nation which was famous for it was the haenyeo in Korea. They collected shells and sponges to sell to others. The Ama Divers from Japan began to collect pearls 2000 years ago. But also the spearfishers around the Mediterranean Sea were important for the historical background for the movement of the apnea sport.