Kinesin-15s are a family of processive, plus-end-directed motors that can function as either homodimers or homotetramers. The simplest oligomerisation state for Kinesin-15 motors is a homodimer: both Xenopuslaevis and Strongylocentrotus purpuratus Kinesin-15, partially purified from meiotic egg extracts, are dimeric with a measured Stokes radius of ~10 nm and a sedimentation coefficient of ~8 S, consistent with being an elongated molecule with a native molecular weight of 334 kDa. Kinesin-15 is a highly versatile motor that is implicated in multiple cellular processes, including mitotic spindle assembly and maintenance and post-mitotic processes such as cell migration, the axonal outgrowth of neurons or the production of red blood platelets from megakaryocytes. Assembly and maintenance of the mitotic spindle requires the balanced activity of three mitotic motors: Kinesin-5, Kinesin-15 and dynein. Finally, Kinesin-15-dependent microtubule sorting and bundling, but not antiparallel sliding, is key to microtubule rearrangements in other organisms.