Microtubules are non-covalent cytoskeletal polymers found in all eukaryotic cells that are involved in mitosis, cell motility, intracellular transport, secretion, the maintenance of cell shape and cell polarization. They are polarized structures composed of α- and β-tubulin heterodimer subunits assembled into linear protofilaments. Microtubules typically consist of 12 or 13 protofilaments aligned in parallel with the same polarity [i.e., one end at which there is a rapid assembly of tubulin (plus end) and the opposite end at which slow assembly or even disassembly occurs (minus end)]. Most microtubules occur as single tubes and form cellular structures such as the mitotic spindle and the interphase network. The properties of microtubules depend on the tubulin isoforms they are made up of — there are three α-tubulins (α1, α2 and α4) and five beta-tubulins (βI, βII, βIII, βIVa and βIVb) — and on how they have been altered by various forms of post-translational modification. Post-translational modifications of tubulin subunits mark subpopulations of microtubules and selectively affect their functions. Microtubule associated proteins offer the potential for new targets for anticancer agents, as they have diverse functions including some actions that stabilize the microtubule, others that are involved in tubulin dissociation, and additional proteins that act as motor proteins to transport substances along the microtubule. This class of anti-cancers agents inhibits cell mitosis by binding to the protein tubulin in the mitotic spindle and preventing polymerization or depolymerization into the microtubules.