The US DoD (Department of Defense) Internet suite of protocols (commonly known as TCP/IP for transmission control protocol/internet protocol) is the de facto open (nonproprietary) standard for computer communications in multivendor and multiadministration networks. However, some feel that protocols based on the open systems interconnection (OSI) model and promulgated by the International Organization for Standardization (ISO) will eventually achieve dominance and enjoy even greater success than TCP/IP. The author explores methods for transition and coexistence between the two protocol suites. He enumerates several approaches, discusses the positive and negative aspects of each, and describes their inter-relationships. Further, although the focus is on the problems of Internet/OSI transition and coexistence, none of the approaches described are unique to this problem. Rather, they are all general solutions to the problem of changing from one protocol suite to another or of having two arbitrary protocol suites coexisting.>