Epigenetics is the study of changes in phenotype of organisms which are not the result of variability of genetic code, rather the change in gene transription. While human genome contains 25,000 genes, human epigenome contains for now still unkownable number of epigenetic marks and mechanisms, from which the best studied are DNA methylation and covalent modifications of histone proteins. Their effect on cell differentiation and organism development during embriogenesis is indisputable. Epigenetic changes are often result of changes in the environment and in some cases they represent a mechanism of adaptation to enviromental fluctuations. This paper's main goal is to describe mechanisms and priciples of epigenetics and emphasize its role in evolution. Epigenetics can explain some differences among organisms that have almost identical genome. Moreover, because of its regulatory role, some scientists theorize that it could be responsible for simultaneous appearance of two or more adaptive characteristics in the same organism during the evolution which could explain the rise of specific complex biological systems.