This chapter examines the state-of-the-art approaches used in the solid-state characterization of pharmaceutical systems using a combination of NMR, X-ray diffraction and computer modelling. Solid-state NMR spectroscopy is highly sensitive to strong and weak crystal packing interactions and is a powerful partner of X-ray diffraction in crystal structure validation/determination; ab initio calculations are very often required to support NMR studies in complex structures, therefore this chapter also highlights the main computational approaches used to extract structural information. The outline of the chapter is as follows. The chapter starts with a high-level introduction into the fields of solid-state NMR, powder and single-crystal X-ray diffraction (Section 6.2), providing a general overview of the main methods and latest developments of each technique in the field of pharmaceutical solid-state chemistry. A vast selection of key application case studies is presented in Section 6.3, ranging from the study of polymorphism (Section 6.3.1), amorphous systems (Section 6.3.2), drug delivery systems (Section 6.3.3), formulated drugs (Section 6.3.4), crystal packing interactions and structure determination (Section 6.3.5). A comprehensive literature selection is provided in each section, highlighting the contributions of each technique (solid-state NMR, X-ray diffraction), their individual drawbacks and the complementarity of their combined use for the characterization and structural elucidation of various pharmaceutical systems.