In the world of pharmaceutical development, powder X-ray diffraction analysis has long been used as a fingerprint method to identify the solid phase of a crystalline material, while thermogravimetric and differential scanning analyses have become the core methods for understanding the characteristics of a solid state form. Informative as they are, these analyses, however, could not provide answers to whether a particular solid phase is indeed a single phase or simply a mixture of two very similar solid state forms. In addition, in cases where we need to distinguish two or more solid state forms that have largely similar PXRD patterns but with subtle differences, we definitely need a tool that allows us to understand the solid forms from a structural level. The objective of this presentation is to show how single crystal X-ray analysis can offer solid state information from the molecular structural level that can be used to understand the bulk properties and characteristics of a crystalline material. In this presentation, we will showcase some examples of how the crystal structure data was used to solve some challenging issues in the development of active pharmaceutical ingredients, such as understanding polymorphs/hydrates/solvates, examining phase purity of bulk material, and projecting the development feasibility of a solid state form.