A swimming pool, swimming bath, wading pool, or simply a pool, is an artificially enclosed body of water intended for swimming or water-based recreation. There are many standard sizes; the largest and deepest is the Olympic size. A pool can be built either above or in the ground, and from materials such as metal, plastic, fiberglass or concrete.

Pools that may be used by many people or by the general public are called public, while pools used exclusively by a few people or in a home are called private. Many health clubs, fitness centers and private clubs have public pools used mostly for exercise. Many hotels and massage parlors have public pools for relaxation. Hot tubs and spas are pools with hot water, used for relaxation or therapy, and are common in homes, hotels, clubs and massage parlors. Swimming pools are also used for diving and other water sports, as well as for the training of lifeguards and astronauts.

Chemical disinfectants such as chlorine, bromine or mineral sanitizers, and additional filters are often used in swimming pools to prevent growth and spread of bacteria, viruses, algae and insect larvae. Alternatively, pools can be made without chemical disinfectants by using a biofilter with additional filters. In both cases, pools need to be fitted with an adequate flow rate.

Natural pools were developed in central and western Europe in the early and mid 1980's by designers and landscape architects with environmental concerns. They have recently been growing in popularity as an alternative to traditional swimming pools.NSPs are constructed bodies of water in which no chemicals or devices that disinfect or sterilize water are used, and all the cleaning of the pool is achieved purely with the motion of the water through biological filters and plants rooted hydroponically in the system. In essence, NSPs seek to recreate swimming holes and swimmable lakes, the environment where people feel safe swimming in a non-polluted, healthy, and ecologically balanced body of water.

Water in NSPs, being 100% chemical free, has many desirable characteristics. For example, red eyes, dried-out skin and hair, and bleached bathing suits associated with overly chlorinated water are naturally absent in NSPs. NSPs, by requiring a water garden to be a part of the system, offer different aesthetic options and can support amphibious wild life such as snails, frogs, and salamanders.

A zero-entry swimming pool, also called a beach entry swimming pool, is a swimming pool having an edge or entry that gradually slopes from the deck into the water, becoming deeper with each step, in the manner of a natural beach. As there are no stairs or ladders to navigate, this type of entry assists older people, young children and people with accessibility problems where gradual entry is useful.