This book explores various aspects of the roles and responsibilities of coast guards, which are increasingly becoming significant today, and sheds light on their authority and limitations in the course of maritime law enforcement. It is unique in its unraveling of all facets of coast guards, focusing on their law enforcement authority and limitations from a practical perspective. It details the principles and procedures that coast guard officers are required to follow in the course of international law at sea by examining treaties, conventions, international rulings, and theories. The text employs a comparative study of national coast guards and a review of cases concerning international maritime law enforcement. It provides practical insights into coast guards and their law enforcement, based on the author's career experience and service as a Commissioner General in the Korea Coast Guard. As such, this book will serve as a good reference in practice and contribute to the formulation of guidelines and criteria of maritime law enforcement of coast guards.