Container closure integrity (CCI) is fundamental for maintaining the sterility and stability of sterile injectable products. Regulators are therefore requiring the execution of robust CCI studies that generate data throughout the product life cycle. Laser-based headspace analysis is a deterministic CCI test technique described in USP <1207> that measures gas which ingresses into a container through a leak defect. Recently, headspace CCI test methods have been developed that both resemble and improve upon the traditional blue dye ingress test. This article describes the headspace gas ingress testing approach which is increasingly being implemented to replace blue dye ingress as a general CCI test method.