Australian species of seahorses (genus Hippocampus) are reviewed and descriptions of nine new species from Australian and adjacent waters are presented: H. jugumus n.sp. (Lord Howe Island), H. biocellatus n.sp. (Shark Bay, Western Australia), H. alatus n.sp. (northern Australia), H. semispinosus n.sp. (Timor Sea, southern Indonesia), H. montebelloensis n.sp. (Monte Bello Islands, Western Australia), H. procerus n.sp. (tropical eastern Australia), H. multispinus n.sp. (northern Australia), H. hendriki n.sp. (northeastern Queensland), and H. grandiceps n.sp. (Gulf of Carpentaria). A total of twenty-four species have been collected in Australian waters, and additional species may be found as these are known to occur in neighbouring waters. Diagnosis and a key for the Australian species are provided.