Axonemal dyneins are generally classified into three types: an outer-arm dynein, a two-headed inner-arm dynein containing two heavy chains, and multiple species of one-headed inner-arm dyneins each containing a single distinct heavy chain. Studies with Chlamydomonas mutants suggest that outer-arm dynein is important for flagellar beating at high frequency, while inner-arm dyneins are important for beating with a proper waveform. Mutant analyses also show that flagella lacking any one type of dynein can beat, albeit slowly, whereas flagella lacking any two types cannot beat. Hence flagellar beating apparently depends on the cooperation between different types of dyneins. In vitro motility assays on isolated dyneins coated on glass slides show that different dyneins have distinct microtubule translocation properties. For example, some inner-arm dyneins rotate microtubules around the long axis during translocation. Other kinds of inner-arm dyneins cause microtubule circling on the surface, most likely by producing a torque. These and other observations indicate that the presence of diverse dyneins is important for proper functioning of cilia and flagella.