A vivarium (Latin, literally for "place of life"; plural: 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.