General aspects of solid-state nuclear magnetic resonance (NMR) of quadrupole nuclei in organic solids, including theoretical background on quadrupole interactions and analysis of the characteristic line shapes that arise from quadrupole and chemical shift interactions, have been described. Two theoretical approaches for spectral simulations, the perturbation and the direct diagonalization methods, are discussed with examples of solid-state 17O (I = 5/2), 33S (I = 3/2), and 79/81Br (I = 3/2) NMR of organic compounds, as well as those of inorganic compounds with larger quadrupole interactions. When the magnitude of the quadrupole interactions is smaller than that of the Zeeman interactions, the perturbation method, in which a mathematical formula can be obtained to express the first and second-order quadrupole interactions under static or magic-angle spinning (MAS) conditions, is applicable. Otherwise, the direct diagonalization method, in which the combined Zeeman and quadrupole Hamiltonian are numerically calculated to provide probabilities for each transition, is applied for spectral simulations. A few experimental techniques to obtain NMR spectra broadened by large quadrupole interactions are briefly described.