Mammalian cells are to a large extent controlled by the environment. Dif- fusible factors (growth factors, cytokines, and hormones) released by oth- er cells in the body bind to and activate receptors localized at the cell sur- face. In the case of the fibroblast growth factor receptor, there seems to be receptors both at the plasma membrane and in the nucleus. Cellular recep- tors control growth, apoptosis, immune function, differentiation, develop- and upon dysregulation, cancer progression and metastasis. Upon li- ment, gand binding, most receptors are internalized. However, the mechanisms of endocytosis are diverse, and receptors are taken into cells from different membrane microdomains. Activation of receptors results in two important interconnected processes, namely, signal transduction and endocytosis. In- terestingly, signal transduction controls endocytosis and endocytosis con- trols signalling. In both processes sequential formation of transient protein machineries is crucial. Currently, characterization of such complex ma- chineries is advancing rapidly. It has recently become appreciated that sev- eral post-translational modifications directly control the affinity of pro- tein-protein interactions. This volume of Current Topics in Microbiology and Immunology focuses on the recent understanding of signalling from in- ternalized activated growth factor receptors. This includes information on pathways by which the rate and specificity of endocytosis and intracellular sorting are controlled. It further includes information on how specialized signalling and trafficking platforms are formed at the plasma membrane and on intracellular vesicles.