Gonium (Greek: γωνία gonia, "angle" or "corner") is a genus of colonial green algae, a member of the order Chlamydomonadales. The genus was first described by Otto Friedrich Müller in 1773, and is among the most common types of algae found in freshwater habitats. It has a cosmopolitan distribution.

Typical colonies of Gonium consist of 4 to 16 cells arranged in a flat plate. Gonium is capable of both asexual and sexual reproduction. Along with other algae such as Volvox, Eudorina and Chlamydomonas, it is a model organism for studying the origins and evolution of multicellularity.

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