Each of the four Vedas has several ‘śākhās,’ branches or recensions. The origin of these śākhās probably lies in the fact that each of the principal sages like Paila or Vaiśampāyana, who transmitted the Vedas, had several disciples. These disciples or their successors did some editing and readjustments of the Vedic mantras to suit the needs of the rites which they performed and upon which the local culture too, sometimes, had its effect. This naturally led to the birth of these recensions.
The name of Āśvalāyana is connected with the Ṛgveda as one of the authors of its śākhās. Not much is known of this Āśvalāyana except that he was the disciple of Śaunaka. Though one Kausalya Āśvalāyana is mentioned in the Praśna Upaniṣad (1.1; 3.1) and an Aśvala in the Bṛhadāraṇyaka Upaniṣad (3.1.1) it is very difficult to establish any connection between them and this Āśvalāyana. The Anuśāsanaparva (7.54) of the Mahā-bhārata mentions one Āśvalāyana as belonging to the gotra or lineage of Viśvāmitra, another great name among the sages. Some scholars opine that he is the same Āśvalāyana, the author of the Ṛgvedic recension.
The Āśvalāyana recension of the Ṛgveda is almost identical with the Śākala recension except that the latter recognizes as canonical, the Vālakhilya supplementary hymn.
One or two works of Āśvalāyana, out of the four attributed to him, are extant now: Āśvalāyana Śrautasūtras and Āśvalāyana Gṛhyasūtras.
The Āśvalāyana Śrautasūtras, which closely follows the Aitareya Brāhmaṇa, consists of twelve chapters. Each chapter is further subdivided into ‘khaṇḍas’ or subsections, the total number of such khaṇḍas being 164. Each khaṇḍa is mostly in the form of a long sentence. The whole work, since it belongs to the Ṛgvedic group, deals mainly with the duties of the ‘hotṛ,’ the priest connected with the chanting of the Ṛgvedic mantras during the sacrificial rites. The sacrifices and rites dealt with in this work are: Darśapūrṇamāsa, Agnyādhāna, Piṇḍapitṛyajña, Āgrayaṇī, Kārīrīṣṭi, Cāturmāsya, Sautrāmaṇi and Somayāga.
The followers of this work are mostly in the southern regions of the river Godāvarī.
The Āśvalāyana Gṛhyasūtras consists of four chapters divided into 48 ‘kaṇḍikās’ or subsections. The topics dealt with in this work are: pākayajña, baliharaṇa, and the ṣoḍaśa (Sixteen) saṁskāras. Rules for the recitation of the Vedas are also given in one of the chapters.
This work gives us the names of many ancient sages which are not found elsewhere.