Basically, any activity that is performed underwater while breath-holding can be considered freediving. However, depending on whether the diver wants to reach a depth, a distance or a time, and what equipment and techniques are used to achieve these goals, the dives will be divided into several categories. The most respected and important categories are the Vertical Immersion categories, while the Horizontal Immersion categories are very popular and easy to practice and the Static Apnea category is more of an exhibition activity than an athletic performance.

Vertical Immersion
In these categories the objective of the diver is to reach a certain depth and they are divided in two main groups: Constant Ballast and Variable Ballast.

Constant Ballast
In this group, the diver must complete the dive and return to the surface carrying with him exactly the same equipment that he took underwater at the beginning of the dive. This applies specially to the weight used for ballast, and thus the category's a name. The allowable equipment is only equipment that remains attached to the diver and which must be powered by the diver's own physical energy. This may include fins, masks, suits, snorkels, or nothing at all. Based on this, there are three different categories in this group:

Equipment Assisted Constant Ballast
Line Assisted Constant Ballast
Unassisted Constant Ballast

Variable Ballast
In this group, the diver may complete the dive without carrying all the equipment throughout the dive, thus the ballast used for the descent can be left at the bottom. In addition, the use of mechanical devices to speed up the descent and ascent may be used under certain conditions. This group is where freedivers can reach truly unbelievable depths, since most of the physical effort is greatly diminished and the most important part is endurance and resisting the crushing pressures found at depth. There are two categories within this group, and they are:

Limited Variable Ballast
Unlimited Variable Ballast

Horizontal Immersion
The goal of this type of freediving is to reach a distance underwater rather than a depth. The depth is not important here, as long as the diver remains submerged while swimming horizontally. This is usually done in a swimming pool, although horizontal immersion is also practiced in the sea or lakes in shallow depths.

Equipment Assisted Horizontal Immersion
Unassisted Horizontal Immersion

Static Apnea
This is one of the oldest forms of breath-holding, though it is debatable whether it can truly be called Freediving, since there is no immersion either for depth or length, and the diver aims for a maximum time result instead, remaining relatively motionless during this whole time. This is done usually floating face down on the surface, although some divers prefer to lay on the bottom of the shallow areas of the pool. The false perception that this category requires "no safety" and can be practiced on a solo basis has lead to many tragic deaths around the world every year, with victims ranging from the very young to very old loosing out on their battle to add a few more seconds to their best time.

Interesting Facts:
- There is no direct correlation between long static apnea results and good vertical or horizontal immersion performances, with several world records in constant and variable ballast having been set by divers who were not proficient in static apnea, while conversely, some persons who are not capable of notable results in depth or length can reach world-class times in static, most notably yoga practitioners of even very old ages.