Adequately considering interactions among IT projects in the process of constructing an IT project portfolio is a necessary condition in value-based IT project portfolio management (PPM). A lot of articles already deal with such interactions, but the literature lacks a common terminology and a structured perspective on the manifold types of interactions and their effects. In this article we present a framework that provides a structured perspective on interactions and thereby supports decision makers in the identification of possible interactions and the selection of appropriate methods for value-based IT PPM.