This chapter reviews the recent progress in the understanding of axonemal dynein in the context of flagellar/ciliary bending motion. It focuses mainly on structural studies using electron microscopy/tomography but also correlates these studies with functional motility assays and theoretical studies. Axonemal dyneins are motor proteins responsible for the generation of force and are one of more than 600 proteins in the flagella/cilia. While the mechanism of the dynein powerstroke itself has been under investigation for a long time, the mechanism that integrates the sliding of individual dyneins into a flagellar/ciliary bending motion is another challenging question that is now attracting scientists. The study reviews the architecture of axonemal dyneins in inner dynein arms and outer dynein arms and discusses their functional significance. Following this, it describes the heterogeneity and asymmetry of the structure and arrangement of dynein in the axoneme. Cryo-tomography has revealed asymmetric structural change of dyneins induced by nucleotides. Also, progress in electron cryo-tomography, genomic studies, and light microscopy has revealed additional exceptional molecular arrangements and structural heterogeneity of dyneins and other proteins in the axoneme. Furthermore, the functional role of dyneins, based on its in situ structure, is explained. Finally, this chapter presents significant questions regarding axonemal dynein structure and function to be addressed in the near future.