Recent regulatory guidance has made clear there is no “gold standard” container closure integrity (CCI) test. An appropriate CCI test method should be applied depending on the specific product container closure system configuration, the stage in the product life cycle, and the testing throughput required. It is therefore considered best practice to create a toolbox of CCI testing methods. Headspace gas ingress CCI testing, using a tracer gas and a CCI test vessel, is capable of generating robust analytical CCI data in all stages of the product life cycle. This Article describes test method development using headspace gas ingress, including a study that illustrates the use and behavior of different positive controls for a empty and product filled vials.