Polymorphism is the ability of a molecule to exist in more than one stable or meta-stable crystalline state. The distinct crystalline forms commonly exhibit differences in pharmacologically relevant properties in solid dose form drugs. These properties include bioavailability,  solubility, rate of absorption, duration, stability, manufacturability, and processibility. The factors influencing polymorphism are numerous, and include the solvents that are used in the formulation, the rate of recrystallization, salt selection, and temperature. Since polymorphism can have profound effects on the properties, and ultimately the manufacture of a compound under development, it is of critical importance to fully characterize and understand a compound’s polymorphic behavior.