This review focuses on the cellular and molecular mechanisms underlying the development of the sensory hair bundle, an apical specialisation of the hair cell that is essential for mechanotransduction. The structure, function and development of the hair bundle is described, with an emphasis on the properties and possible roles played by the different link types that interconnect the individual elements of the hair bundle - the multiple stereocilia and the single kinocilium. Studies of mouse and zebrafish mutants have revealed that several classes of molecule are required for the genesis and maintenance of hair-bundle structure. These include cell surface molecules that are associated with the different hair-bundle links, along with myosin motors, scaffolding proteins and an actin cross-linker. Finally we consider how differences in the form and shape of hair bundles within and between different sensory organs are generated.