Despite the collaboration between reproductive medicine and molecular biology, the global fertility rate has been consistently declining during the last few decades. It might be partly explained by the prevalence of infertility, one of the most painful social-medical problems in gynecology. About one in ten couples suffer from infertility. Oocytes represent a female matter of reproductive function. Doubtless, the follicular pool of both ovaries correlates with the rate of infertility, which naturally increases with age. However, some factors (traumas and diseases, genetic disorders, chemotherapy, assisted reproductive techniques, abnormal preantral folliculogenesis) have an impact on the ovarian reserve and lead to infertility. The quality and the number of oocytes could be considered the best potential predictors of female reproductive age and, consequently, the chance of becoming pregnant. This Methods Collection covers biomarkers of the ovarian reserve, some pathological conditions that affect the ovaries, and features of ovarian aging. Comprehensive knowledge of clinical aspects, animal experiments, morphological and immunohistochemical studies, and genetics allow an analysis of the linkage between follicles in the ovaries and reproductive health. This Methods Collection will be attractive for medical doctors as well as scientists focusing on reproductive medical problems.