Central to all cilia is the axoneme, one of the most geometrically complex and structurally conserved macromolecular machines found in nature. Using high-resolution cryo-EM techniques we are beginning to resolve this beautiful structure in atomic detail. Recently, we have determined structures of ciliary doublet microtubules, radial spoke complexes, and microtubule-bound axonemal dyneins from the model organism Chlamydomonas reinhardtii. These studies have revealed new insights into the principles that guide the assembly of the axoneme, the mechanisms that regulate ciliary motility, and the disease mechanisms of human ciliopathies. This project is an ongoing collaboration with Dr. Rui Zhang and Dr. Susan Dutcher at Washington University in St. Louis.