Many methods have been developed to examine the bulk properties and underlying molecular interactions of biomolecular condensates that form through liquid–liquid phase separation (LLPS). Phase separation assays using bright-field imaging or fluorescence microscopy track droplets over time and can assess the effect of various conditions on LLPS, measure droplet formation and dissolution kinetics, and test the miscibility of differentially labeled molecules. Fluorescence recovery after photobleaching (FRAP) and microrheology by particle tracking probe the diffusion of molecules within droplets, while droplet fusion assays, right angle imaging, and surface wetting determine droplet surface tension.