In the inner ear of the mammals, transduction of the input sound signal is carried out by two classes of sensory hair cell. The cochlea uses outer hair cells to operate as part of a fast local mechanical feedback loop, preamplifying the sound in the duct, and uses inner hair cells to act as sensory input to the auditory nerve. Cochlear amplification itself depends on basolateral mechanisms in the outer hair cell, with a possible involvement of the apical transducer system. Both hair cells types have a mechano-electrical transduction complex located at the tips of the apical stereocilia. Stereocilia are complex organelles, with at least 100 distinct associated proteins involved in their make-up and function. Mouse models of hearing disorders provide some clues about transduction and those with stereocilial and synaptic deficits have been particularly helpful. Despite much effort, the channels in the transduction complex (now thought to contain at least five distinct components) have resisted identification. Single channel recording from mammalian hair cells favours a heteromeric assembly of distinct TRP channels; the gating mechanism details remain unclear. TRPA1 although present in hair cells but appears not to be essentially involved in the complex. In addition, the mechano-electrical channel properties vary between inner and outer hair cells as well as along the cochlea. Such gradients parallel K channel (e.g. Kv7.4) composition in the basolateral membrane of outer hair cells where a higher K channel number is observed in those cells used in high frequency coding.