A detailed taxonomic revision of the siphonous marine green algal genus Caulerpa J.V.Lamour. (1809a) in northern (tropical and subtropical) Australia, covering mainland shores, continental islands, coral reefs and offshore territories, is presented. Sixteen species and 10 varieties of Caulerpa are described and illustrated. One variety, C. cupressoides var. urvilleana (Mont.) I.R.Price is a new combination. A lectotype is proposed for C. racemosa (Forssk.) J.Agardh var. macrodisca (Decne) Weber Bosse. One species of Caulerpaceae long included in Caulerpa, but more recently placed in a separate genus, Caulerpella, as C. ambigua (Okamura) Prud homme Lokhorst, is also treated for completeness. The present publication will complement Womersley s (1984) account of southern Australian taxa of Caulerpa.