A vivarium (Latin for 'place of life'; pl. vivaria or vivariums) is an area, usually enclosed, for keeping and raising animals or plants for observation or research. Water-based vivaria may have open tops providing they are not connected to other water bodies. An animal enclosure is considered a vivarium only if it provides quality of life through naturalistic components such as ample living space and natural decor that allow and encourage natural behaviours. Often, a portion of the ecosystem for a particular species is simulated on a smaller scale, with controls for environmental conditions such as temperature, humidity and light.

A vivarium may be small enough to sit on a desk or table, such as a terrarium or an aquarium, or may be a very large structure, possibly outdoors. Large vivaria, particularly those holding organisms capable of flight, typically include some sort of a dual-door mechanism such as a sally port for entry and exit, so that the outer door can be closed to prevent escape before the inner door is opened.

Some vivaria can be subcategorized according to the habitat or lifeforms enclosed within. A vivarium that contains multiple components may be named according to its primary component, or simply called a vivarium. Each subcategory can refer to either an individual enclosure, or a facility that encompasses numerous like enclosures.

An aquarium (aqua = water) is a water-filled enclosure housing aquatic plants and/or animals such as fish. A bioactive aquarium would additionally house micro-organisms such as beneficial bacteria, and janitor animal species such as caridean shrimp, boxer shrimp, algae-eating snails and burrowing snails. At least one side of an aquarium is glazed to allow viewing of the aquatic habitat from the side as though viewing from underwater. Aquaria are further subcategorized by temperature (cold water, tropical) and salinity (freshwater, brackish, marine).

A Dutch aquarium (origin = Netherlands) is an underwater garden that features plants, with minimal visible hardscaping and few fish. It is terraced or the back-wall is lined in moss to prevent view through the rear of the aquarium.

A terrarium (terra = land) is an enclosure for a land habitat for animals, plants, fungi, lichens or any combination thereof. A bioactive terrarium would additionally house soil microorganisms and janitor animal species such as springtails and terrestrial isopods. It is distinct from a pot plant or animal cage by being enclosed to an extent to permit maintenance of temperature and humidity levels different from the ambient environment. Terraria are further subcategorized by biome (tropical/temperate desert, rainforest, grassland, etc.). A terrarium may feature a horizontal land surface, an escarpment (steep slope or cliff), or a fossorial (underground) section.

A Wardian case is a 19th-century sealed terrarium used for transport or display of plants or small animals such as moths under conditions where ventilation was more harmful than beneficial such as where ambient conditions were too saline, dry or polluted to support delicate species.

A bottle garden is a small sealed glazed terrarium, an actual glass bottle or otherwise, in which all water and nutrients that will be required for future growth of the plant(s) and soil microorganisms are sealed into the vessel at the time of planting, the only required care being management of light and temperature.