Living eukaryotic cells must carry out and coordinate an enormous number of biochemical reactions in order to obtain and convert energy to usable forms, break down and interconvert organic molecules to synthesize needed components, sense and respond to environmental and internal stimuli, regulate gene activity, sense and repair damage to structural and genomic elements, and grow and reproduce. This level of complexity requires that biochemical reactions be highly organized and compartmentalized, and this is the major function of cell organelles and the cytoskeleton. Cells have elaborated an elegant cytoplasmic membrane system composed of the nuclear envelope, ER, Golgi apparatus, and associated endocytotic, endosomal, lysososomal, and secretory vesicles and compartments. These membranes serve to both organize and compartmentalize biochemical reactions involved in protein and lipid synthesis, targeting, and secretion. The cytoskeleton not only facilitates cytosolic molecular interactions, but also serves to organize the entire cytoplasmic membrane system. The key to cellular life is organization, and eukaryotic cells display a remarkably rich and elegant architecture to carry out the demands of life.