The assembly of biomolecular condensates is driven by liquid–liquid phase separation. To understand the structure and functions of these condensates, it is essential to characterize the underlying driving forces, e.g., protein–protein and protein–RNA interactions. As both structured and low-complexity domains are involved in the phase separation process, NMR is probably the only technique that can be used to depict the binding topology and interaction modes for the structured and nonstructured domains simultaneously. Atomic-resolution analysis for the intramolecular and intermolecular interactions between any pair of components sheds light on the mechanism for phase separation and biomolecular condensate assembly and disassembly. Herein, we describe the procedures used for the most extensively employed NMR techniques to characterize key interactions for biomolecular phase separation.