The first parts of the present text are devoted to a "passive" cochlea, i.e., to cases in which the mechanical energy generated by "active" outer hair cells is absent or negligibly small. Passive human cochleae were studied, e.g., in the post-mortem experiments of von Békésy, who found that tones generate, in the cochlear channel, travelling hydrodynamic surface waves which are similar to waves propagating on the ocean. In spite of the fact that the travelling-wave energy starts to be transformed into frictional heat at the cochlear base already, the velocity amplitude of the basilar-membrane oscillation increases with increasing distance from base. At some place, namely at the "passive peak", that increase stops, and at greater distance from base the amplitude quickly drops to small values. At high (low) tone frequency, the distance from base of the passive peak is short (long).Additional topics treated in this book: the outer hair cells and the "active" response peak generated by them; evanescent cochlear waves; high-frequency plateaux; cochlear maps; certain forms of tinnitus; otoacoustic emissions; frequency glides.The readers are expected to know high-school biology, physics, and mathematics. Exercises and their solutions are included at the end of most chapters.