The microtubule (MT) cytoskeleton plays a crucial role in a number of cellular functions including cytoplasmic organization, intracellular transport, cellular polarity, and cell division. Microtubules are linear polymeric structures composed of heterodimers of α- and β-tubulin with a class of specialized proteins, the microtubule-associated proteins, typically being present. Microtubules are dynamic structures that undergo repeated rounds of assembly/disassembly. The half-life of MTs, an index of their dynamics (i.e., assembly-disassembly), has been estimated from studies of single cells in culture and typically ranges from ≈ 5 - 20 minutes depending on the cell type. These dynamic properties of MTs have been explained in terms of the “dynamic instability” model. Five parameters have been used to describe dynamic instability of MTs: (1) elongation velocity; (2) shortening velocity; (3) nucleation frequency; (4) catastrophe frequency; and (5) rescue frequency. Catastrophe is the transition from elongation to shortening while rescue is the transition from shortening to elongation.