By Fran DeGrazio and T. Page McAndrew, West Pharmaceutical Services, Inc. Qualification, and demonstration of fit-for-purpose, for a drug product vial/stopper/seal primary package system comprises many factors: protection, compatibility, safety, and performance. One of the subcategories is container closure integrity (CCI), which is the topic of this article. CCI is essential to protect the drug product through shelf life, and to demonstrate an integral system to regulatory agencies.