The doctoral dissertation “Pactum antichreticum” is primarily focused on the research of the institute of pactum antichreticum by taking a comparative historical and positive legal approach. The first part of the doctoral dissertation is devoted to the analysis of the genesis of the institute of pactum antichreticum through pre-Roman legal systems of Sumerian, Akkadian, Mesopotamian and Greek cultures as well as the legal nature and characteristics of this institute in Roman law. Emphasis is placed on the distinction between pactum antichreticum, as a pact that can be added to contracts recognized by civil law, and an innominate contract of antichresis that represents the do ut facias type of contract. The second part of the doctoral dissertation is aimed at identifying the degree of reception of the Roman institute of pactum antichreticum in civil law codifications of the 19th century and comparative analysis of the antichresis contract in the positive law of France, Spain, Italy and selected countries of Latin America. The purpose of this research is to offer a de lege ferenda solution for the Croatian legal system that (de lege lata) does not regulate the antichresis contract and prohibits pactum antichreticum with the mortgage agreement.