Many drugs are unstable in aqueous solutions, and drying is commonly used to improve their storage stability and shelf life. Freeze-drying is the most common drying method for parenteral pharmaceutical dosage forms, including both small molecular weight drugs and biologicals. Alternative vacuum drying technologies have also been introduced, although predominantly for research and development purposes. The presentation focuses on freeze-drying, starting with a brief overview of lyophilized (freeze-dried) products and corresponding manufacturing processes. The importance of pressure control during all three stages of freeze-drying (i.e., freezing, primary drying/ice sublimation, secondary drying / desorption of non-frozen water) is emphasized.