Mitochondria are „central energy station” of the cell, a cellular organelles whose most important role is the production of energy necessary for all cellular processes (cellular growth, development, metabolism, etc.). Significance of these organelles is that they contain their own DNA material. Also, reactive oxygen species (ROS), aggressive particles that cause mitochondrial DNA (mtDNA) damage, i.e. the damage of mitochondrial genome, are produced in mitochondria. As a damage result, mtDNA mutations occur and cause the onset of severe and rare multisystem mitochondrial disorders, syndromes and diseases which are usually specific for a particular age group. Since mtDNA is inherited exclusively from mother, mitochondrial diseases are associated with so-called maternal inheritance. mtDNA mutations are present in many tissues, where the energy needs of these tissues largely determine the level of their presence. Therefore, diseases caused by mutations of mtDNA most often affect the central nervous system and muscles. In this work, the structure and function of mitochondria, structure and inheritance of mtDNA, as well as their mutations and the role in development of mitochondrial diseases, are studied.