Publisher Summary This chapter focuses on the developments in the techniques of solid state nuclear magnetic resonance (NMR). The most important obstacle to the wider application of solid state NMR is the low sensitivity of the technique. This arises from the small magnitude of the energy separation among the nuclear spin states in a magnetic field, giving only a small difference in population. The transfer of magnetization from an abundant spin, normally protons, to a rare spin, such as 13C, has been of major importance in allowing the development of solid state NMR. Without this increase in sensitivity, the range of experiments would be greatly restricted. Cross-polarization has been achieved in three ways: first, using adiabatic demagnetization in the rotating frame (ADRF) where dipolar order is created from the proton magnetization followed by its transfer into the rare spin; second, by spin-locking in the rotating frame and transferring the magnetization by applying matched rf fields to both the spin systems meeting the so-called Hartmann–Hahn condition; and third, by a solid effect involving the saturation of forbidden transition. The chapter discusses high-temperature superconductors, 1H NMR of inclusion compounds, 1H MAS NMR imaging, and heteronuclear couplings by rotational-echo double-resonance (REDOR).