In contrast to cytoplasmic dynein, there are a number of axonemal dynein isoforms in cilia and they have fixed loci on microtubule doublets. Axonemal dyneins form arrays on microtubule doublets with a periodicity of 24. nm (outer-arm dyneins) or 96. nm (inner-arm dyneins). While the AAA ring domain of axonemal dynein displays high homology to cytoplasmic dynein and therefore their basic power stroke mechanism seems similar to that of cytoplasmic dynein, there should exist a unique mechanism to integrate the power stroke of various dyneins into a well-orchestrated beating motion of cilia. In this chapter, we review recently obtained knowledge about the axonemal dynein, mainly in structural aspects from molecular to ultrastructural levels.