In the last years, the software development based on mobile agents has received important attention because it introduces a new development paradigm for widely distributed and heterogeneous systems. Up to now, the usual approach for mobile-agent applications development has been focused on the implementation phase, mainly because of the vast lack of suitable modeling techniques or methodologies in the domain. In this sense, the development of powerful abstractions for the modeling of mobile agents becomes increasingly important. In this article, we present an approach to deal with the lack of appropriate concepts and notations in the standard Unified Modeling Language (UML) to capture relevant abstractions for the modeling of mobile-agent features. This approach is materialized by a coherent and comprehensive set of views and models, which extends UML contributing to the analysis and design phases of mobile-agent applications development.