Here, we describe 16 species of true oysters from Thai waters. They are widely distributed on various intertidal and subtidal substrates in the Gulf of Thailand and in the Andaman Sea. The different species were identified on the basis of their shell morphology, and their characteristic features are described. We have also included notes on their habitats and distribution. The species belonging to the following families are described in this book: family Gryphaeidae: Hyotissa hyotis, Parahyotissa imbricata; family Ostreidae (subfamily Crassostreinae): Crassostrea belcheri, C. bilineata, 5accostrea cucullata, 5. echinata, and 5. forskali; (subfamily Lophinae): Lopha cristagalli, Dendrostrea folium, D. rosacea*, D. crenulifera*, D. sandvichensis*, and Anomiostrea caralliophila*; (subfamily Ostreinae); Nanostrea exigua*, Pfanostrea pestigris, Pustulostrea tuberculata*. The 6 species indicated with asterisk were recorded for the first time in Thailand.