Interrupter resistance (Rint) is one of the easiest ways to assess respiratory resistance during tidal breathing with minimal subject cooperation. This article enclosed current knowledge on technical and practical aspects such as how to measure Rint, and how to calculate Rint. Issues on repeatability of the technique and bronchial responsiveness are discussed. Recommendations on Rint technique are provided on behalf of the Interrupter Technique Subcommittee of the ATS/ERS Working Group on Infant and Young Children Pulmonary Function Testing.