The existence of a yoga-system with six limbs or parts instead of eight as in Patañjali's Yogasūtra has been known long since. Not known has been the multitude of texts with the six-limbed yoga in Hinduism. They can be arranged in three groups: (1) texts with a number of limbs other than six or eight, (2) texts which only mention the aaga-yoga but do not give details, (3) texts which treat the six-limbed yoga in full. Here we have two subgroups: (a) the Āsana-, (b) the Tarka-group (in this we can distinguish two divisions). The yoga of the last group is quite similar to the aaga-yoga of Buddhist Tantrism (regarding the order of limbs). In this article only questions can be formulated because the main problems cannot be answered at present. It is the first of a series giving materials for a history of the aaga-yoga.