Yoga instructor courses were traditionally part of residential training, yoga studio or ashram activities. Yoga instructor diplomas were not common before the late 1900s. The traditional aspirant used to travel to India for the direct lineage with a Guru, an apprenticeship, and his blessing. It is still possible to enroll in courses in India, to advance your understanding of the philosophical underpinnings of yoga as a field of education, personal enlightenment, and holistic health. Today, organizations that handle yoga teacher credentialing courses are generally defined as teacher training programs.