This atlas aims to provide a ‘one-stop’ reference source of basic data on tropical marine ciliates that should be used for researchers worldwide. As one of main components, ciliates play vital roles in the microbial food web. Studies of ciliate diversity are, however, constrained by a lack of modern monographs and guides for the identification of tropical marine ciliates. Therefore, an image-rich guide or atlas like this book will undoubtedly be of great benefit for those who are not trained in ciliate taxonomy but who encounter ciliates in disciplines such as ecology, environmental biology, aquaculture and other related fields. We have carried out in-depth studies on ciliates along the coastal area of South China Sea for more than ten years and got a lot of ‘first-hand’ data. This atlas will assemble diagrams and photomicrographs of 315 free-living species of ciliate that have been found in the coastal area of the South China Sea. To be reader-friendly, habitats, ecological features and key references as well systematics will be provided for every species.