Many of the molecules that comprise the “tip link” are associated with Usher syndrome [37, 40]. Mouse models for Usher syndrome show perturbed stereocilia, mis-positioned kinocilium, and fragmented bundles with abnormal numbers, shapes, and orientation [41, 42]. The Usher type 1 proteins (cadherin 23 and protocadherin 15) are observed in the stereocilia tips with transient lateral links along stereocilia as early as E16.5 [41, 43–45]. The second type of link, ankle links, is formed [43] at birth and the Usher type 2 proteins (VLGR1, whirlin, and usherin) localize to these links [46–50]. As described before, the “tip link” itself is composed of homodimers of cadherin 23, bound at its carboxy-terminal ends to the upper tip link density (UTLD) and protocadherin 15, bound at its carboxy-terminal ends to the lower tip link density (LTLD). The two homodimers interact at their amino-terminal ends forming the structural link between adjacent stereocilia and between the tallest stereocilia and the kinocilium [51, 52] (Fig. 4.1). Myosin VIIA, SANS, and harmonin-b localize to the UTLD of mature hair cells and anchor the cadherin23 homodimer to the actin cytoskeleton necessary for the sensitivity of hair bundles to mechanical stimulation [53, 54]. In contrast to the well-known UTLD assembly, the molecular composition of the lower tip link density is less characterized. The cytoplasmic domain of protocadherin 15 is anchored to the LTLD, where it interacts with the tetraspanin TMHS. TMHS mutant mice are deaf, and fast adaptation is abolished. It has been proposed that TMHS may facilitate both the transport and assembly of the, as of yet unidentified, mechanotransduction channel which would be functionally coupled to the tip link apparatus via protocadherin 15 interaction [55, 56]. Although molecular assembly of the tip link and its connection to the actin cytoskeleton has been characterized step-by-step, its clear role in mechanotransduction is under question. Interestingly whirlin plays a role for the localization of both usherin and VLGR1 and for the stereocilia formation. Thus, some of the Usher proteins function to not only assemble the links but also transport link molecules and maintain the integrity of the links. Elucidating the exact roles of the Usher proteins may prove to be more difficult though. The protein themselves are large and exist as a number of isoforms [57–59]. Thus, for functional characterization, each isoform should be analyzed separately which necessitates the generation of isoform-specific reagents, such as mutants, antibodies, and over-expression models. Such elucidation is necessary if we want to recreate the machinery that generates stereocilia in cells.