One of the major goals of the Viewpoint framework is to allow for heterogeneous and distributed implementation of viewpoint-based tools. This poses a number of challenges on the integration of tools into a viewpoint-based environment. We review different infrastructures that could be deployed for tool integration and argue that the OMG/CORBA architecture provides the best support for achieving heterogeneity and distribution. We then discuss how viewpoint-based tools can be integrated on the basis of CORBA. This involves the integration of different viewpoint representations as well as their presentation at user interfaces.