The fast motility of the outer hair cell is important for distinguishing the tones and thus important for recognizing speech. This motility is extremely fast and unlike other biological motilities which depend on chemical energy. To clarify this mechanism, we carried out experiments which characterize the electrical and mechanical properties of the membrane of this cell. These experiments showed that the cell membrane is elastic for brief stresses and that the cell motility is driven by a "molecular motor" embedded in the cell membrane. We have shown that this membrane motor is based on a direct electromechanical coupling and that it undergoes a conformational transition to which both membrane voltage and tension are important. This was demonstrated by measuring the membrane capacitance while the membrane tension and the membrane potential were changed. The membrane capacitance decreased at physiological membrane potentials on membrane stretch. These decreases are dependent on the membrane potential imposed. Based on these observations, we predicted that tension shifts the membrane potential at which the membrane capacitance peaks. This shift was subsequently confirmed by other groups. We then proposed a model incorporating the results of these individual experiments to describes the motility of the entire cell. This model predicted that the force generated by the cell is up to 0.15 nN/mV, which was consistent with available in vivo estimates. This value was recently confirmed by direct force measurements. From these examinations we can conclude that this motility is directly driven by the electrical energy available at the plasma membrane and that we have obtained an adequate model for describing the mechanism. We are currently studying various factors which control this motility. For example, membrane plasticity becomes important when strain is prolonged. We found that one of the of such characteristic relaxation time constants is about 30 seconds. We are also studying how this cell can modulate the vibrations in the inner ear. These efforts would enable us to identify the cellular and molecular bases for fine tuning of the ear, essential for communication.