The problem of NPAs is almost in every bank no matter public or private, national or foreign, rural or urban. This problem relates with the credit issuance and the risk associated with the payback and recovery process. The causes of a loan turning into NPA can be many such as frauds, business cycles, corruptions etc. Out of them one of the important cause is the lack of effort and due diligence done during the pre-sanction process. Conducting the due-diligence process in the inattentive manner leads to rising in the levels of NPA in banking sector. This paper reviews the relevant articles and papers published addressing the problems of non-performing loans in the Indian banking sector during the period 2001- 2019. Empirically we identify the causes of the occurrence of non-performing loans to help us demonstrate the above.