Abstract The X.25 protocol was first standardized over a decade ago by the International Telegraph and Telephone Consultative Committee (CCITT). Since then, many enhancements to the basic protocol have been made. One of the most significant and recent changes has been the addition of a dial in/out capability. More importantly, and as a result of some of these changes, the field of application of X.25 has been greatly expanded. No longer a protocol used only to access “X.25 networks”, it is now being used in Local Area Networks (LANs) as well as in the emerging Integrated Services Digital Networks (ISDNs). It has also become part of the work known as Open Systems Interconnection (OSI). The International Organization for Standardization (ISO) has collaborated with CCITT in these developments of the X.25 protocol, resulting in several ISO standards and CCITT Recommendations that enable universal connectivity. This article examines the evolution of X.25 with particular attention to the last eight years.