Clathrin-mediated endocytosis is a key membrane trafficking pathway in eukaryotic cells. It is critical for nutrient uptake, signal transduction and cellular homeostasis. The formation of endocytic vesicles is driven by a complex proteins machinery, which is composed of about 50 different proteins. These cytosolic proteins assemble transiently at the endocytic site and then return back to the cytosolic pool after vesicle budding. In this project we have focused on the poorly understood cytosolic pool of the endocytic proteins. We have characterized cytosolic protein concentrations, diffusion constants and protein-protein interactions fluorescence correlation and cross-correlation spectroscopy methods. By identifying the protein complexes that are present in the cytoplasm we have defined the “building blocks” that are used for the assembly of the endocytic machinery at the endocytic sites. We further focused our studies on one of the identified proteins complexes: self-assembled Ede1 protein. We showed that oligomerization of Ede1 is critical for its function as a scaffold protein that recruits endocytic adaptors and cargo molecules. These data provide a basis for quantitative understanding of the assembly of the endocytic machinery.