The Volvocales is a large group including some familiar green algae such as Chlamydomonas and Volvox. The volvocalean algae is very common in freshwater, but some species inhabit in marine and on land. Many species are photosynthetic but some species are colorless heterotrophic (Polytoma, Polytomella). Chlamydomonas reinhardtii is widely used as a model organism in biology.

Many species are unicellular flagellate, but many flagellate coenobial (e.g. Gonium, Pandorina, Volvox), coccoid (e.g. Chlorococcum), sarcinoid (e.g. Desmotetra), palmelloid (e.g. Tetraspora) and filamentous (e.g. "Gongrosira") species are also known. The flagellate cell is naked or covered by glycoprotein cell wall. In some species (e.g. Phacotus), calcium carbonate is deposited in cell wall. The flagellate cell possesses two (sometimes four) flagella inserted apically. The basal bodies are usually displaced clockwise, but some (early divergent?) species possess directly opposed basal bodies (Hafniomonas, Carteria). Asexual reproduction by means of binary fission, zoosporogenesis or sporogenesis. Sexual reproductions by isogamy to oogamy are reported. The volvocalean algae with sexual reproduction show haplontic life cycle in which the zygote (usually resting stage) is only diploid stage.