The present paper is an attempt to sort out the wide variety of concepts used in connection with systems integration. and to give an overview of the f i e l d . The p a p e r is primarily descriptive. but also to some extent prescriptive. Four arpects of systems integration are addressed: Integration technology, Inlegration architecture, Semantic integration and User integration.Our main message is that systems integration is diffiult and complicated. and that there are no obvious shortcuts. In addition, integralion is made difjicult by most existing systems being twt particularly integration friendly. In the paper we give some guidelines to how systems should be built to be more integration friendly. We also give some recommendations on how existing system may be made more integration friendly. To ab integration in practice, one has to know all the ins and outs. This paper tries to point out some of them.