We present a review of nonlinear optical properties of liquid crystal light-valves, in particular describing how wave-mixing experiments are implemented in these systems. We show several different applications based on optical wave-mixing occurring in the liquid crystal layer. Slow-light effects are obtained by performing two-wave mixing with a continuous reference beam and a pulse signal, providing group velocities as low as fractions of mm/s. Correspondingly, the group index becomes very large, a property that can be exploited to realize interferometric systems with enhanced sensitivity. Based on the same effect, nonlinear detection of the Sagnac effect and accelerometer systems are realized. Finally, adaptive holography in the liquid crystal light-valve is presented, together with the detection of acoustic waves.