The messenger paradigm is one of the earliest models which propose the exchange of code to implement computer communication. Code becomes mobile and mobile code is now considered a promising alternative for the implementation of distributed applications. One application of mobile code is in the implementation of software agents which themselves are used to implement complex distributed applications. However, efficient execution environments for mobile code are needed before mobile code can be considered a true technology for distributed applications. Our messenger project has focused at identifying and providing, both at the operating system level and at the language level, the necessary mechanisms for the efficient support of distributed applications built with messengers. Since the project has reached a global consistent point, this paper, that can be considered as a position paper, provides an overview of the theoretical and practical aspects of the whole project. The main result of our work is the definition and implementation of an environment for the execution of messengers and the corresponding language for expressing the messenger behavior, called respectively the M0 platform and the M0 language. In both the language and the environment, minimality and efficiency have been the leitmotiv.