This publication outlines the main aspects and issues to be considered when developing and improving in-service inspection effectiveness in nuclear power plants (NPPs). It also provides a status of in-service inspection practices in NPPs in selected IAEA Member States, evaluating criteria for effective traditional in-service inspection and introducing the concept of risk-informed in-service inspection. The strategies for improving in-service effectiveness discussed in this publication consider the entire framework of in-service inspection, including effective selection of the proper inspection scope, inspection interval and non-destructive examination efficiency.