This paper describes how object-oriented concepts can be used throughout system development for integration purposes. Based on the distinction of physical and conceptual integration the concept of object wrapping is discussed for the integration of non-object-oriented systems. By regarding applications as high-level objects, i.e. wrapped applications, integration is achieved by modelling so-called integration relationships between these wrapped applications. While in conceptual integration redundancy and message passing relationships are specified, in physical integration message passing relationships only are implemented. The paper finally outlines theactivities of the conceptual integration process.