Visible spectroscopy in the spectral region from ω0/2 to 2ω0 has been shown to be a powerful method of explaining the existence and the consequence of three-wave parametric instabilities in laser-produced plasmas. Experiments at 1054 and 351 nm have shown evidence for Brillouin, Raman, 2ωp, and ion parametric-decay instabilities. The details of the spectra can be used to deduce temperatures at quarter critical from ω/2 spectra and the Mach number and temperature from Brillouin scattering.