Regular and prolonged swimming in the sea, in addition to the pleasure it provides, has beneficial effects on health, but it can also present certain risks. This book explores the physiological effects of swimming, particularly in cold water ( 10 to 14 °C), in the light of recent data. The author presents a complete picture of the benefits and risks of this activity. He offers advice and recommendations for safe swimming in the sea in all seasons. This book is intended for those who are interested in this activity and want to start in the best conditions, but also for experienced swimmers who want to go further in the understanding of their practice.