Embryonic stem cells (ESCs) self renew their population, also they are pluripotent which means they can differentiate into any given cell type. In specific culture conditions they remain undifferentiated. On the cellular level pluripotency is determined by many transcription factors, e.g. Sox2, Nanog, Klf4, Oct4. Epigenetic regulation is also crucial for both self renewal and pluripotency. This review focuses on epigenetic mechanisms, among them DNA methylation, posttranslational histone modifications, ATP dependent chromatin remodeling and miRNAs interactions. These mechanisms affect embryonic stem cells functions keeping them poised for differentiation.