A central practice to both premodern and modern yoga, prāṇāyāma (lit. "breath control") is practised in yoga classes worldwide. Just like prāṇāyāma, the notion of prāṇa (lit. "breath", "vitality") has a longstanding history in South Asia. From 1850 onwards the practices are subject to change, and prāṇa and prāṇāyāma are reinterpreted in light of the Hindu reform, nineteenth-century occultism, science, physical culture, medicine, and hygiene. In Yoga Breath: Prāṇa and Prāṇāyāma in Early Modern Yoga, Kraler for the first time traces the history of yoga's breathing techniques between 1850 and 1945. In doing so, Kraler demonstrates the centrality of prāṇa and prāṇāyāma for understanding modern yoga's praxeological, philosophical, political, and religious thrust. Part 1 "Contexts and Concepts" delves into transnational cultural and religious networks that enable the rise of prāṇa and prāṇāyāma within modern yoga. It also provides an overview of premodern prāṇāyāma and explores the notion of prāṇa as part of a cosmological outline of influential protagonists like Vivekananda. Part 2 "Pioneers and Practices" sets the stage to analyse the intricacies of prāṇāyāma practice and discusses the impact of ten influential yoga pioneers that were active in India and/or the United States, among these Vivekananda, Krishnamacharya, Yogananda, Sivananda and Yogi Ramacharaka. This book provides deep insights into the various practices, functions, and interpretations of prāṇa and prāṇāyāma. Engaging one of modern yoga's key practices, it not only offers a thorough academic analysis, but also responds to a growing interest in breath cultivation worldwide.