Non-cellular life, or acellular life, is life that exists without a cellular structure for at least part of its life cycle. Historically, most (descriptive) definitions of life postulated that an organism must be composed of one or more cells, but this is no longer considered necessary, and modern criteria allow for forms of life based on other structural arrangements.

The primary candidates for non-cellular life are viruses. Some biologists consider viruses to be organisms, but others do not. Their primary objection is that no known viruses are capable of autonomous reproduction: they must rely on cells to copy them.

Engineers sometimes use the term "artificial life" to refer to software and robots inspired by biological processes, but these do not satisfy any biological definition of life.