This paper presents a model of incremental change that consists of concept location, impact analysis, actualization, change propagation, supporting refactorings, and testing. Repeated incremental change is the foundation of an agile process called Conceptbased Incremental Development (CID). A case study of a Point of Sale system illustrates the usefulness of CID. The paper argues that CID complements those agile processes that concentrate on team and management issues, and therefore can be combined with them.