A Vast literature known as upa-purana is a valuable record of Indian life and thought. Hence they are as important as the Puranas are for the reconstruction of the ancient Indian history. But due to the high importance attached to the eighteen Mahapuranas and also on account of the prefix upa attached to the Purana to characterize those Puranic works which are different from the Mahapuranas, their value is not recognized by the scholars. In his scholarly work entitled "Studies in the Upa-puranas" Dr. Hazra has rightly observed, that some of them are much earlier than many of the Mahapuranas, and that like the extant Mahapuranas. They are of capital importance not only for the study of the social and religious institutions of the Hindus from the pre-Gupta period downward but also for varied information of literary, historical, geographical and cultural interest."
Though the number of Upa puranas is fairly large yet the orthodox tradition limits their number rigidly to 'eighteen'. A number of lists of eighteen Upa-puranas occur in the Kurma, the skanda, the Garudas the padma, the Devibhagavata etc. They are greatly divergent in nature. In fact they give us the titles of many more Upa-puranas than eighteen. Besides the Upa-puranas enlisted, there were many other, some of which are available in printed forms, some still exists in manuscripts, some are known only from references and quotations and some must have been listed altogether without leaving any trace of their existence.
It is not an easy task to fix the date of these Upa-puranas. The evidences which can be adduced from the Puranas and other sources are perhaps sufficient to show that the date of the formation of the group of eighteen Upa-purnas as found in the Kurma-purana should be placed notlater than 850 A.D. The Upper limit of this date seems to be supplied by Matsya Purana chapter 53 which by its mention of only those four Upa-puranas viz. Narasimha, Samba, Nandi and Aditya, whichwere well-established in society, betrays its knowledge of a few more Upa-Puranas and at the same time its ignorance of any group of 'eighteen.' The date of formation of the group should be placed approximately between 650 and 800 A.D.
A tradition recorded in the puranas holds that the sages proclaimed the Upa-puranas after listening to the eighteen Puranas from vyasa. This tradition assigns the Upa-puranas to a date posterior to that of the Puranas and consequently to a position inferior to that of the later.
The Matsya-purana calls the Upa-puranas mere subsections (upabheda0 of the Puranas and propounds the theory that any Pauranic work which will be found to be different from the Puranas must be known to have originated from one or other of these Puranas. The Extant Saura Purana holds that the Upapuranas are mere supplements (Khila) to the principle purana. But this theory is not accepted by the Upa-puranas themselves In large number of cased the Upa-puranas are found to style themselves simply 'Purana' and not Upa-purana try to pass on their own merit without caring to attach themselves for the sake of authority to any of the principal Puranas, and in few cases they even vie with the principle Puranas by laying claim to their position. Sometimes they claim to be superior to the Mahapuranas. Moreover the other Upa-puranas do not give any list of Upa-Puranas nor do they seem to be familir with their common title 'Upa-purana' or with the theory of their origin which makes them mere supplements to the principal Puranas.