The selection of the most favourable criterion for the achievement of an equal position of non-testamentary heirs in inheritance proceedings is a repeated issue throughout history, and the reason for that are the influence of social and historical changes, on the one side, and the necessity to adjust the system of non-testamentary inheritance, on the other. The non-testamentary inheritance right has been subjected to large, significant and radical changes during the development of the Roman law, thus creating legal rules and practice, many of which form an integral part of many modern, actual legislations. With the development of non-testamentary inheritance, legal practices and legal rules thus have been created and gradually adapted to the requirements of the correspondent period. In addition to the elementary notions and characteristics of inheritance (introducing the issue), this thesis presents the development of non-testamentary inheritance and alterations during crucial historical periods of the development of the Roman law from the adoption of the Code of the Twelve Tables to the Code of Justinian, proceeding, comparing and concluding with the organisation of non-testamentary inheritance to the rules of modern Croatian legislation.