In consequence of Abdel-Hamid and Madnick's pioneer work on system dynamics modeling of software development processes, there is a great number of recent publications dealing with the simulation of the software development process (or sub-processes of it) with system dynamics. Projects that contract third parties to develop the software are even more unpredictable and underestimated by management than pure development projects, and, thus, there is also a need to model and simulate these projects. This article deals with the design of system dynamics models of the unexplored domain—at least with respect to system dynamics—of software acquisition; a framework is described, which captures causal structures common to all models of acquisition projects. Outputs of one concrete instance of the framework are presented finally. Copyright © 2004 John Wiley & Sons, Ltd.