Isolated microtubules and kinesin spontaneously self-organize in vitro creating assemblies that resemble bundles of cilia that undergo synchronous beating. The major components are fluorescent taxol-stabilized tubulin, biotin-kinesin, and streptavidin. The movie shows tubulin trapped at the air-glass interface of an air bubble that has been confined in a 10-μm-thick chamber. The microtubules nucleate assemblies of active bundles perpendicular to the edge of the bubble, and provide important insights into the mechanism of synchronized ciliary beating observed in vivo.