This chapter discusses an ontological approach to tutoring actions design as a special case of target-world modeling. Although a lot of research on the learner model has been done to improve the adaptivity of intelligent tutoring systems (ITSs), the modeling of tutoring actions has not been sufficiently investigated. The authors have been performing ontological modeling of learning/instructional theories to remedy this situation. Intelligent tutoring systems must have a good number of primitive actions to generate intelligent actions. Paying close attention to the importance of modeling tutoring actions, we have developed an ontology of learning/instructional theories, named OMNIBUS, in the ITS domain. Drawing on our long experience in ontological engineering research, this chapter discusses the modeling of tutoring actions as well as target-world modeling per se, using an example of learning/instructional actions from the OMNIBUS/SMARTIES project.