Wild fighting fish species belonging to the genus Betta inhabit fresh waterbodies of Southeast Asian countries and are found in the Indochinese mainland, the islands of the Kingdom of Brunei, Indonesia and Malaysia. The best known species of the genus is Betta splendens, the colourful Siamese fighting fish, from which ornamental variants are bred and have proved to be a commercial success internationally. These fishes display territorial aggressiveness. Two modalities of paternal care are employed by the species, nest-building and mouth-brooding, whilst caring for fertilized eggs and newly hatched fry. Both types of fishes are found in most of these ASEAN countries mentioned above. With recent taxonomic studies, there are now 73 wild valid species in total; 18 that are bubble-nest builders and 55 mouth brooding species, a number of which have been listed as endangered. These fishes have adapted to various habitat conditions and can be found in a variety of water types. Betta habitats can be waters that are very still or slow running, soft, slightly brackish or even acidic. Though generally preferring
the tropical climate, some can survive temperatures below 20°C. Species identities have so far been established mainly based on morphological criteria, but some have now been identified morphologically as well as genetically. Recent DNA works indicate that the validity of some species and their phylogenetic relationships should be re-examined. This article aims to make an updated review of all Betta species in terms of biodiversity, phylogenetic relationships and distribution in Southeast Asia.