Tamp filling processes are widely used for the filling of powders into hard gelatin capsules, whereby capsule fill weight is controlled by the formation of a loosely packed plug of material that is dispensed into the capsule shell. To rationally design formulations for tamp filling processes the formulator must have an intimate knowledge of the synergy between machine parameters and powder properties and the corresponding effect on product quality. However, despite ubiquitous use throughout the pharmaceutical industry, relatively little is understood about the design of powders for tamp filling processes. The aim of the following review is to summarize the published literature to date from a formulation design perspective and to provide a framework for future scientific research.