The digital video sequences presented in this section visualize the dynamic activity of endosomes, which were targeted with mEmerald fused to the early endosomal marker Rab5a, in relation to the nucleus, tagged with mApple fused to H2B. The formation of endosomes occurs through a complex family of processes collectively referred to as endocytosis. The three key types of endocytosis are pinocytosis, phagocytosis, and receptor mediated endocytosis. Similar to the complexity of their origin, the activity of endosomes once they are released into the cytoplasm is varied and requires multiple steps to complete.