There is increasing recognition of the potential benefits of mobile agent technology for distributed and mobile applications. However, thus far there has been only very limited consideration of the specific requirements for conceptual level modeling of agent mobility to support analysis and design of such applications. Furthermore, the fragmented nature and inconsistent terminology characterizing such research to date complicates the effort to understand and compare the work. An ontology describing the abstract concepts and inter-relationships required to model agent mobility is presented in this paper, intended to serve as the necessary first step to providing conceptual level support for mobile agent applications and as a cogent means of comparing existing work in the area.