The tumor suppressor breast cancer 1, early onset (BRCA1) plays an important role in maintaining the genome integrity, actively participating in DNA repair via homologous recombination. The level of functional final BRCA1 protein is precisely regulated in cells. Epigenetic regulation of BRCA1 gene expression is one of the most important mechanisms for BRCA1 level fine-tuning. In this review the main epigenetic mechanisms of BRCA1 expression regulation are presented, including DNA methylation, histone covalent modifications, and regulation with transcription factors. Another important function of BRCA1 emerging in recent years is its role in the regulation of breast cancer stem cell development. Moreover, based on its multiple functions, BRCA1 is also arising as a powerful biomarker. In particular, it could be used as a prognostic marker of the course of the disease and as a predictive marker of the efficiency of platinum-based chemotherapy.