The term “cytoskeleton” is often used as if it described a single, unified structure, but the cytoskeleton of neurons and other eukaryotic cells comprises three distinct, interacting structural complexes that have very different properties: microtubules (MTs), neurofilaments (NFs) and microfilaments (MFs). Each has a characteristic composition, structure and organization that may be further specialized in a particular cell type or subcellular domain. The defining structural elements have long been identifiable in electron micrographs (Fig. 8-1), and a considerable amount is known about the detailed organization of these components in neurons and glia. Each set of cytoskeletal structures is considered in turn.