Article is dedicated to the institution of succession reserve. The author highlights the main historical period for the formation of this institution under Russian and Ukrainian law, from the pre-revolutionary Russian Empire through the Soviet period and then up to modern Ukraine and the Russian Federation. The Article shows in details the main legal regulations and principles which established the reserve system according to the newly written Russian and Ukrainian civil codes. These include, the problem of establishing a group of persons with the right to “minimum inheritance” (practically speaking, the part of group of inheritors ab intestato). Also the article considers the legal methods of calculation of legal portion, possibilities for reduction and deprivation of the reserved portion.