The effective control of attentional focus is an essential requirement in mental reasoning based on mental models and men tal images, as well as in the interaction with external diagrams. In this paper, we argue for spatial or ganization principles common to various mental subsystems that entail a non-centralistic con trol of focus. We give a brief overview of mental spatial rea soning and present a review of psy chological findings related to cognitive con trol. We review existing mod eling approaches that realize control of focus in imagery, scene recognition, and men tal animation. Based on these founda tions, we identify basic spatial or ganizing principles that are shared by the diverse subsystems col laborating in mental spatial reasoning. We discuss the implica tions of these principles in the frame work of a computational modeling ap proach and give an outline of the con ception of control of focus in our com putational architecture Casimir.