In this paper I present Swami Vivekananda’s teachings on the theory and practice of prāṇāyāma. Although Vivekananda is widely known as a teacher and scholar who taught yoga and Vedanta in India and later in the West, and his collected works of more than three thousand pages have been published, there are surprisingly few scholarly works about him. The bibliography I compiled lists only sixteen works of secondary literature published in English between 1990 and 2025. Moreover, only two of these works explicitly address the topic of yogic breathing. Further, some interpretations heavily draw on critical theory and postmodernist perspectives, seeking a political dimension to his work rather than a spiritual mission in the West. Hence, although Vivekananda is a key Indian thinker, spiritual leader, and philosopher who was instrumental in introducing Hinduism, particularly Vedanta and yoga, to the Western world, scholarly research on his ideas, and especially the concept of prāṇāyāma and its spiritual dimensions, remains largely unexplored. My objective is to clarify this concept, as presented in his book Raja Yoga and in several shorter texts: “Breathing,” “Concentration and Breathing,” and “Practical Religion: Breathing and Meditation,” published as Lectures and Discourses in the Volume 1 and 6 of The Complete Works of Swami Vivekananda. The research questions I wish to address concern Vivekananda’s understanding of prāṇāyāma and how this concept relates to his overall work on raja yoga.