Upa Puranas occupy a very important place among Hindu scriptures. There are about eighteen or even more Upapuranas or minor Puranas. They are equally important as the major puranas but some scholars treat them with lesser importance.
Majority of the Upapuranas appeared several centuries after the Mahapuranas or eighteen major Puranas. But there are some minor puranas whose antiquity is as same as the major puranas like Narasimha, Nandi, Samba and Aditya Puranas.
Most of the Upa Puranas are treated as less important because they are taken as subsections of major puranas.
The eighteen Upapuranas are
Santakumara, Narasimha, Skanda,Sivadharma, Ascharya, Naradiya, Kapila, Vamana, Asunas, Brahmanda, Varuna, Kalika, Maheshwara, Samba, Saura, Parasara, Maricha and Bhargava.
The contents of the minor puranas are generally the same as those of the major Puranas.