This book is based on a Special Issue called "Marine Compounds and Cancer" (http://www.mdpi.com/journal/marinedrugs/special_issues/marine-compounds-cancer) of the open access journal, Marine Drugs (ISSN 1660-3397), which was running for two years (2013-2015). It comprises 39 articles in total, a quarter of which are reviews, summarizing the current state of the art in different topics of marineanti-cancer agents. It covers the full scope from agents with cancer-preventive activity, to novel and previously characterized compounds with anti-canceractivity, both in vitro and in vivo, and the latest status of clinical development of marine agents used in clinical trials.