We use structural and biochemical methods to study how cytokines activate receptors to initiate precise signaling events across the cell membrane. Receptor tyrosine kinases (RTKs) are key players in the control of a wide range of cellular processes including proliferation, differentiation, migration and survival. They are composed of an extracellular domain to which specific ligands bind, a single-pass transmembrane helix, and an intracellular tyrosine kinase domain flanked by regulatory regions. We seek to understand how the extracellular event of ligand binding to the receptor is translated into an accurate intracellular response. We are also interested in structural investigations of coordinated signaling through assemblies of RTKs and co-receptors. Through the parallel use of X-ray crystallography and single-particle electron microscopy, we address basic mechanistic questions concerning the early stages of cell signaling.