Fast electro-optical switching with planar nematic liquid crystals in multipass and also Fabry-Pérot modulators has been realized. By using short driving pulses of 150V, we achieved microsecond switching times for nematic planar cells (NPC) and even sub micro-second switching in case of nematic Fabry-Pérot modulators (NFPM), which have been applied as active Q-switches in Nd:YAG solid state lasers. Four different resonator configurations have been investigated. Typically, giant pulses of 35–70 ns duration (FWHM) with energies between 10–25 mJ are emitted. A rather plain Q-switch resonator design consists of only two optical components: a cholesteric liquid crystal polarizing mirror and a reflecting nematic liquid crystal modulator.