Research in the Veatch Laboratory is aimed at understanding how the physical properties of lipid and lipid mixtures influence cellular functions that occur at the plasma membrane. Lipid bilayer membranes containing cholesterol can support two coexisting liquid phases, called liquid-ordered and liquid-disordered. There is evidence that the presence of this phase transition impacts the organization and function of plasma membrane proteins because the cell plasma membrane is poised in the vicinity of a miscibility critical point. We are currently exploring the physical basis of functional lateral heterogeneity in living cell membranes using a variety of experimental and theoretical approaches, including super-resolution fluorescence localization microscopy, fluorescence imaging of fluctuations in isolated plasma membrane vesicles, and Monte Carlo modeling of basic signaling processes.