If the Internet is seen as a single, vast, programmable machine, what is the proper programming paradigm to facilitate development of the new applications it must offer? This state-of-the-art survey deals with this question. The situation we face is similar to that in the 1960s, when a new hardware/software architecture was introduced and it took some time for the programming-language and operating-system specialists to come up with the proper programming paradigms. Now we have the new and exciting paradigm of mobile computing, where computations are not bound to single locations but may move around at will to best use the available computer network resources. This paradigm will have a profound impact on the way distributed applications, in particular Internet applications, are designed and implemented.