This paper analyzes the institute of loan (mutuum) and related contracts in Roman legal tradition, with a focus on the current regulation of loan in contemporary Croatian law. Loan (mutuum) is a contract with foundations which were established in Roman law and which developed from a moral (natural), unenforceable obligation to a legally regulated institute with corresponding legal protection. The main characteristics of loan (mutuum) in Roman legal tradition are that it is a contract re (obligation arose from an object delivered), unilateral binding effect, stricti iuris obligation, and the possibility of agreeing on interest rates with prescribed limitations. Additionally, the paper deals with certain particular questions associated with the development of the contract of mutuum in Roman law (for example the Senatus consultum Macedonianum) and the maritime loan (fenus nauticum) with all its specificities. Furthermore, the text particularly analyses the contracts of stipulatio and expensilatio as contracts related to mutuum, since they were often concluded alongside or instead of a loan. Loan in contemporary Croatian law corresponds in greater part to mutuum from Roman legal tradition, with an important distinction that it is conceived as a consensual contract. The text further deals with the objects of contemporary loan, obligations of the contracting parties, types of loan, interest rates with prescribed limitations, usurious loan agreements (which are also a criminal offense), and the credit agreement as a variation of the loan agreement, as well as the similarities and differences between these contracts.