Abstract: The version negotiation of the present invention insures that there will always be an expected data and control interface between a Dynamic Link Library (DLL) and an application program that relies on the DLL. The application program makes an initial call to the DLL that specifies the DLL version with which it prefers to operate. The DLL compares this preferred version number to the version numbers that it supports, which are in a supported DLL version table within the DLL. If the preferred version matches one of the table entries, then the DLL returns an "OK" flag to the application program. In this case, the application program goes on with its normal execution. However, if the preferred version is not supported, then the DLL returns to the application program a "not OK" flag and a list of versions that it does support from its table of supported versions. In response, the application program looks up the versions on this list in a table of compatible versions contained within the application program.