Software engineers of multi-agent systems (MASs) are concerned with the design and implementation of the mobility issues in addition to the agents` basic functionalities and other agent-related concerns. As the agents` complexity increases, mobility issues cannot be modularized based only on object-oriented (OO) abstractions and mechanisms. Besides, some programmers frequently evidence the presence of mobility tangling and scattering problems on their systems. Despite these problems, MAS developers have mostly relied on application programming interfaces (APIs) OO from mobility platforms and on the use of the Java programming language. The result is the production of MASs that are difficult to understand, maintain, and reuse. This work presents three main contributions. Firstly, an analysis of existent solutions for modularization of mobility issues. Besides, the proposal of the ArchM software architecture and the AspectM framework, both based on aspects, which support: (i) improved modularization of the mobility issues, that is, a clean separation between the mobility-specific concerns and the other agent concerns, (ii) a seamless introduction of code mobility into stationary agents, and (iii) a flexible integration with multiple mobility platforms. The aspect- oriented software development (AOSD) is a new paradigm with abstractions and composition mechanisms that support an improvement of reuse and maintainability of systems. The benefits of the AspectM framework are illustrated through two case studies and through use of two mobility platforms.