  Solid-state NMR spectroscopy is a powerful technique for the characterization
of the atomic-level structure and dynamics of materials. Nevertheless, the use
of this technique is often limited by its lack of sensitivity, which can
prevent the observation of surfaces, defects or insensitive isotopes. Dynamic
Nuclear Polarization (DNP) has been shown to improve by one to three orders of
magnitude the sensitivity of NMR experiments on materials under Magic-Angle
Spinning (MAS), at static magnetic field $B_0 \ge 5$ T, conditions allowing for
the acquisition of high-resolution spectra. The field of DNP-NMR spectroscopy
of materials has undergone a rapid development in the last ten years, spurred
notably by the availability of commercial DNP-NMR systems. We provide here an
in-depth overview of MAS DNP-NMR studies of materials at high $B_0$ field.
After a historical perspective of DNP of materials, we describe the DNP
transfers under MAS, the transport of polarization by spin diffusion and the
various contributions to the overall sensitivity of DNP-NMR experiments. We
discuss the design of tailored polarizing agents and the sample preparation in
the case of materials. We present the DNP-NMR hardware and the influence of key
experimental parameters, such as microwave power, magnetic field, temperature
and MAS frequency. We give an overview of the isotopes that have been detected
by this technique, and the NMR methods that have been combined with DNP.
Finally, we show how MAS DNP-NMR has been applied to gain new insights into the
structure of organic, hybrid and inorganic materials with applications in
fields, such as health, energy, catalysis,optoelectronics etc.
