This paper describes ongoing research focused on two critical problems posed by the interconnection of a massive number of computer systems. The interconnection may be achieved through wide area or local area networks. The two problems considered in this research are as follows: (1) performance analysis of the protocols used in an internetwork connecting thousands to millions of nodes, and (2) application development in a massively distributed, heterogeneous environment where components implemented in different programming languages must be integrated and/or reused. The performance analysis problem is addressed by employing large-scale parallel simulation, extended finite state machines and objected-oriented simulation techniques. The approach to solving the application development problem is based on an environment which exploits the synergism between object-oriented programming and layered communication protocols (specifically, OSI).