A type of NMR spectroscopy using a solid sample. Anisotropic interactions between nuclei, which are usually averaged by Brownian motion in liquid samples, cause significant line broadening in solid state NMR, but can be averaged to zero by spinning the sample very rapidly at the magic angle (54.74 deg. with respect to the direction of the magnetic field). Cross polarisation is used to enhance the signal from weakly coupled nuclei such as 13C nuclei.