Mobile agents are a useful paradigm for the development of complex Internet applications. However, the effective development of mobile agent applications requires suitable models and infrastructures. This paper proposes an organizational approach to the design and development of mobile agent applications and describes an infrastructure designed to support such approach. The approach models the Internet as a multiplicity of local and active organizational contexts, intended as the places where coordination activities of application agents occur and are ruled. The MARS coordination infrastructure supports the development of mobile agent applications by implementing organizational contexts in terms of programmable tuple spaces. An application example related to the use of mobile agents to access and organize tourist information is introduced and discussed through the paper to clarify our approach and to show its effectiveness.