The procedures for Yagas  are mostly similar throughout the country and are well classified. Based on several factors, Somayaagams are of various types, out of which, one is Agnishtomam and the other, Athiraathram. Athiraathram itself can be further divided, based on several factors.

Jyothishtomam: The core or basic entity (Moola Prakruthi) of all Somayaagams is called Jyothishtomam, which involves four Sthomams. Sthomams are collections of the musical Saamavedam combined with the Sthothrams ( hymns of divine praise ) and Sasthrams ( collection of hymns ) of Rigvedam. These Sthomams lead the doer to "Jyothiss" or enlightenment (Prakaasam, Agni), and that is Jyothishtomam. Each of the four Sthomams in Jyothishtomam denotes the number of Sthothra-Sasthrams taken from Rigvedam. They are the three-branched Thrivruth (consisting of nine Riks), Panchadasam (15 Riks), Sapthadasam ( 17 Riks) and Ekavimsam (21 Riks).

The Prakruthi - Vikruthi Classification: Depending on the ending process, Jyothishtomam has four Prakaarams with Agnishtomam as the Prakruthi (Entity). The Samsthhas (ending) of Jyothishtomam can be in seven different ways and thus six more kinds of Yaagams can be derived out of Agnishtomam. Agnishtomam is the first Samsthha. Agnistomam is a Jyothishtomam which ends with a Stuthi (hymns in praise) for Agni (Fire) as Devatha. There are three Vikruthis (attributes) for Agnishtomam which are Ukthyam, Shodasi (or Sholasi) and Athiraathram (Agni). Ukthyam, which is a Vikruthi, now acts as a Prakruthi (entity) to produce further Vikruthi (attrribute) called Vaajaapeyam. Similarly, Athyagnishtomam is derived from Shodasi and Aapthoryaamam, from Athiraathram. Thus, in all, Jyothishtomam is divided into seven Samsthhas. It may be noted that Agnishtomam is purely Prakruthi, while Ukthyam, Shodasi and Athiraathram are Prakruthi-Vikruthis (as they are Vikruthis of Agnistomam as well as Prakrithis of the last three), while the last three are purely Vikruthis (as they do not produce further Yaagams). The knowledge of these inter-relationships is essential for the successful performance of Yaagams, and are clearly defined in Kausheethaka Braahmanams.

The Sasthram-based Classification: Yaagams ending with the 12th Sasthram is Agnishtomam. A Yaagam with the 12 Sasthrams of Agnishtomam and three additional Sasthrams of the Hothans (15 Sasthrams in all) is Ukthyam, while one more Sasthram (16 Sasthrams) makes it Shodasi. Addition of 13 more Sasthrams to Shodasi will be Athiraathram (29 Sasthrams). Vaajapeyam has 17 Sasthrams and is an extension of Shodasi by one more Sasthram. Athyagnishtomam is one without Ukthyam (3 Sasthrams) but ending with Shodasi-Sasthram and having a total of 13 Sasthrams. As an extension of Athiraathram, if one Sasthram for each of the four Rithwiks is added, it becomes Aapthoryaamam (33 Sasthrams).

Agnishtomam ->12 Sasthrams

Ukthhyam - 12 Sasthrams of Jyothishtomam + 3 Sasthrams for Hothans - 15 Sasthrams

Shodasi - 15 Sasthrams of Ukthyam + 1 additional Sasthram - 16 Sasthrams

Athiraathram - 16 Sasthrams of Shodasi + 13 additional Sasthrams - 29 Sasthrams

(Some Sasthrams are chanted at night; so the name Athiraathram)

Vaajapeyam -16 Sasthrams of Shodasi + 1 additional Sasthram - 17 Sasthrams

Athyagnishtomam - No Ukthyam but ends with Shodasi Sasthram - 13 Sasthrams

Aapthoryaamam - 29 of Athiraathram + 4 additional Sasthrams - 33 Sasthrams

Suthyam-days based Classification: The most important stage of Somayaagam is the Suthyam (stage 4, discussed later), although there are several days of rituals (Karmams) preceding it to purify the performer in order to qualify him to do the Yaagam. Based on the number of Suthyam days, Yaagam may be categorised into three : Ekaaham - 1 day (example : Agnishtomam, Udbhith, Abhijith), Aheenam - 2 to 12 days (example : Athiraathram, Paundareekakrathu ) and Sathram - more than 12 days (example : Raajasooyam - 18 months, Aswamedha Yaagam - 12 months). Sathrams are again classified as Raathri-Sathrams (12 to 100 days; counted in terms of days) or Samvatsara Sathrams (more than 100 days; counted in terms of years).