Our human anatomy dictates that we should attempt to breathe through our noses whenever possible as a way to preserve our health; yet the vast majority of exercisers breathe through their mouths during exercise. While breathing orally allows for an increase in ventilation, increased work capacity, and initially perceived comfort, doing so also predisposes us to a variety of potential health problems. However, paradoxically, recent research, as well as long-held anecdotal observations in a small number of elite endurance athletes, suggests that humans can adapt to breathing nasally during exercise at all levels of intensity. This is true despite reduced ventilation and without loss in performance ability. Doing so engages the health-protecting conditioning aspects of the nasal anatomy, as well as improving one's physiological economy. This book systematically addresses the research examining the possibility of adapting to nasal breathing during exercise as well as the health and performance-related implications of such a choice. It further suggests practical approaches based on the author's 19 years of experience breathing nasally as a competitive triathlete, as well as publishing research on the topic himself. The book is intended for those scientists, health professionals, exercisers, and athletes interested in both a better understanding of the topic and/or in implementing such an approach in their exercise program.