Cells have an array of protein receptors on the plasma membrane that help process environmental cues. The spatial and temporal arrangement of these receptors is critical to function, but the chemical forces driving this organization are not well understood. This talk will focus on receptor tyrosine kinases (RTKs), which are transmembrane proteins that regulate cell growth, proliferation, and differentiation. Several RTKs are oncogenic and are targeted in next generation anti-cancer drug development. The degree to which these oncogenic mutations affect the local network of interactions between RTKs has not been explored beyond a few high-profile examples. We use pulsed interleaved excitation fluorescence cross-correlation spectroscopy (PIE-FCCS) to resolve membrane protein mobility, concentration, and monomer/dimer/oligomer distributions. I will describe ongoing work in my group to resolve the network of interactions between EGFR, HER2, HER3 and HER4, and how this network responds to oncogenic mutations.