The origins of the CAPI-Association go back to the year ´89, when the three German ISDN-card-manufacturers AVM, Stollman and Systec established the "CAPI-Arbeitskreis". This working-group arouse from the need of a vendor-independent programming-interface for personal-computer based isdn-solutions. Soon many other manufacturers of isdn-hardware, developers of isdn-applications and even the predecessor of the "Deutsche Telekom AG", the "Deutsche Bundespost Telekom" joined in. This working group established an application programming interface for ISDN called CAPI (COMMON-ISDN-API). This interface has had an incredible success. Almost every single ISDN-application for personal-computers developed in Germany is based on CAPI. An increasing number of developments in other European countries are now also CAPI-based. The CAPI-working-group continued its work defining extensions to the original specification.

The extension include support of different operation-systems (DOS, Windows, OS/2, Netware, Unix), fax-capabilites, direct-dialing-in, dtmf-detection... When the European d-channel- protocol DSS-1 was introduced, the working-group defined an extension for CAPI 1.1 to support this protocol-stack without requiring changes in any existing application.

Soon the need for an updated version of CAPI became visible. The new interface specification was designed to meet all necessary points of Q.931 or ETS300102 compliant ISDN-protocol-stacks. The new specification was named COMMON-ISDN-API V2.0 (CAPI 2.0). At about this time the working-group, which was to this point just an informal assembly of companies and organisations wishing to participate, decided to "legalize" its status to become an association ("eingetragener Verein / e.V" corresponds roughly to the term association under German jurisdiction).