Excipients, which often make up the major proportion of tablet dosage forms are materials that can exist in different solid phases, such as polymorphs, hydrates, amorphous forms or mixed phases. Compendial and manufacturer specifications are typically focused on particulate and chemical attributes. However, variation of excipients at the molecular level can impact their performance characteristics, functionality, and formulation manufacturability. The objective of this presentation is to highlight the diversity of solid form variation in tableting excipients and provide a framework for categorizing their phase compositions. A secondary objective is to relate these categories of phase variation with their propensity for transformation due to manufacturing stresses.