A bank guarantee is an important instrument for securing financial obligations in legal transactions, creating security and trust between the contracting parties. This paper analyzes the legal aspects of a bank guarantee as a security interest, including its legal nature, types of guarantees, as well as the rights and obligations of the contracting parties. Special focus is placed on the analysis of domestic legislation in the Republic of Serbia and comparative legal practice, highlighting the similarities and differences of approaches across different jurisdictions. The paper also examines the role of bank guarantees in international transactions with reference to relevant international conventions and regulations, especially in the context of globalization of markets. The aim of the paper is to provide a comprehensive overview of the legal framework that governs the issuance and enforcement of bank guarantees and to identify challenges and opportunities for improving this financial instrument in practice. Based on the analysis, recommendations are made for legal entities to optimize the use of bank guarantees in business transactions.