Sea slugs are tiny, cryptic, brilliantly coloured and highly diverse in nature. Yet sea slugs in India are little known entities. Mostly lacking a shell but adorned with spectacular colours, they use an assortment of defences to keep their predators at bay, even reusing their toxic chemicals and stinging cells. With specific food and dwelling needs, they form important indicators of a habitat's health. But, so far, only about 400 species are known from the Indian coastline. This field guide provides up-to-date information about 361 species, their geographical range and how to identify them. The guide is replete with 666 colour photos of live animals, making it highly engaging. Written in a lucid style, this user-friendly guide will be of interest to students, teachers, researchers, policy makers, divers and beachcombers.