Book excerpt: In 2015 three leading scientific experts on nudibranchs and sea slugs collaborated to produce a comprehensive guide for divers and scientists to the Indo-Pacific region. After only three years, Nudibranch and Sea Slug Identification Indo-Pacific has sold out and become outdated due to the discovery of new species and numerous changes to the taxonomy of these organisms. On 1 November 2018, a new 2nd Edition will be realeased -- updated and reorganised, including 185 new species. Among other features, the new edition includes additional photographs of species, an identification key, and an up-to-date classification. The Indo-Pacific represents the largest expanse of tropical ocean in the world, stretching from the Indian Ocean coast of southern Africa and the Red Sea to the central Pacific of the Hawaiian Islands, Easter Island and the Marquesas. This region supports the most diverse marine fauna of any place in the world for most groups of marine organisms. The nudibranchs and sea slugs are no exception to this rule; there are about 3,000 described species of these organisms in the world and at least 40% of these have been found exclusively in the Indo-Pacific tropics. This book illustrates 2,138 Indo-Pacific nudibranchs and sea slugs, including many undescribed species.