The special physical and functional properties ascribed to lipid rafts in biological membranes reflect their distinctive organization and composition, properties that are hypothesized to rest in part on the differential partitioning of various membrane components between liquid-ordered and liquid-disordered lipid environments. This review describes the principles and findings of recently developed methods to monitor the partitioning of membrane proteins and lipids between liquid-ordered and liquid-disordered domains in model membranes, and how these approaches can aid in elucidating the properties of rafts in biological membranes.