Genetic and biochemical studies in yeast and animal cells have led to the i
dentification of many components required for endocytosis. In this review w
e summarize our understanding of the endocytic machinery with an emphasis o
n the proteins regulating the internalization step of endocytosis and endos
ome fusion. Even though the overall endocytic machinery appears to be conse
rved between yeast and animals, clear differences exist. We also discuss th
e roles of phosphoinositides, sterols, and sphingolipid precursors in endoc
ytosis, because in addition to proteins, these lipids have emerged as impor
tant determinants in the spatial and most likely temporal specificity of en
docytic membrane trafficking events.