Resonance energy transfer (RET) is a widely used technique in biochemistry to study biomolecular structure and dynamics, providing information on distances ranging from 10 to 100 Å. The method is based on the detection of fluorescence changes due to energy transfer between donor and acceptor molecules. The theoretical framework, known as Förster theory, describes the rate of energy transfer in terms of the distance between the donor and acceptor, with the critical distance, \( R_0 \), determined by the spectroscopic properties of the chromophores. Practical aspects of RET include sample preparation, Förster distance determination, methods for detecting energy transfer, and data analysis. Recent advances in instrumentation and data analysis have enhanced the reliability and applicability of RET, making it a valuable tool for studying macromolecular assemblies and their functions. Applications of RET include qualitative and quantitative studies, average distance determination, and distance distribution analysis, providing insights into molecular interactions, conformational flexibility, and dynamic processes in biological systems.Resonance energy transfer (RET) is a widely used technique in biochemistry to study biomolecular structure and dynamics, providing information on distances ranging from 10 to 100 Å. The method is based on the detection of fluorescence changes due to energy transfer between donor and acceptor molecules. The theoretical framework, known as Förster theory, describes the rate of energy transfer in terms of the distance between the donor and acceptor, with the critical distance, \( R_0 \), determined by the spectroscopic properties of the chromophores. Practical aspects of RET include sample preparation, Förster distance determination, methods for detecting energy transfer, and data analysis. Recent advances in instrumentation and data analysis have enhanced the reliability and applicability of RET, making it a valuable tool for studying macromolecular assemblies and their functions. Applications of RET include qualitative and quantitative studies, average distance determination, and distance distribution analysis, providing insights into molecular interactions, conformational flexibility, and dynamic processes in biological systems.