Solid form screening is commonly performed to find a candidate with optimal properties for early development or to find a form with different properties to improve a formulation in later development. A variety of screens can be performed including polymorph, salt, co-crystal, amorphous, and amorphous dispersion. X-ray powder diffraction (XRPD) is commonly used at various stages of screening to identify and characterize new forms. It is also used to help evaluate other properties, such as physical stability and manufacturability, in order to choose the best form for development. This paper discusses the use of XRPD during screening and form selection of pharmaceutical materials.