Ovaries as the primary female reproductive organs have many function. The most important functions of ovary are production and secretion of female reproductive hormones as well as oogenesis. Ovarian cancer is the most lethal malignant neoplasms of the female reproductive system. Ovarian surface epithelial tumors are the most common ovarian tumors and account for more than 85% of all malignant tumors. Despite numerous studies being undertaken to resolve the pathogenesis and tumorigenesis of ovarian cancer which would help to develop screening methods and assist in diagnosing early stage disease, the mortality rate from this disease has not been changed in the last 50 years. Until recently it was considered that ovarian cancer is a single disease and was treated according to that knowledge. Recent studies have shown that ovarian cancer is heterogeneous disease that involves various histological types of tumors that differs in degrees of maturity, clinicopathologic, molecular features and responses to treatment. Based on results of these studies the new model of ovarian cancer pathogenesis has been proposed. According to that surface epithelial tumors of the ovary are classified into two broad categories: type 1 and type 2, based on their clinicopathologic features and characteristic molecular changes. These new insights have contributed to a different approach in diagnosing of ovarian cancer involving morphological and additional molecular analysis, all with the aim of individualized therapeutic approach to each patient.