In this paper, some fundamental aspects of the semantics of rule-based systems are sketched and related to the semantics of visual models. A rule-based system comprises a set of rules and some control conditions including descriptions of initial and terminal configurations. Semantically, the rules specify a binary relation on configurations of some kind by means of rule applications which are restricted according to the control conditions. As visual models are usually represented by diagrams, graphs or similar configurations, the rule-based setting can be employed to provide visual models with semantics.