In 1985, Nippon Telephone and Telegraph (NTT) needed a small digital switch for deployment in rural areas of Japan, and wanted to add another supplier of digital switching equipment that could team with NTT in the same manner as their other suppliers. NTT embarked on a long-term plan to build a teaming relationship with Northern Telecom that has culminated in a volume supply agreement for 1.5 million lines of DMS-10 equipment. An essential requirement for Northern Telecom to be successful in its relationship with NTT was to provide the high-quality standard expected by NTT and demanded by the Japanese end user. This paper puts forth the strategy followed by Northern Telecom and NTT to build a Joint Development process with specific focus on achieving a continually improving standard of software quality. It will trace the evolution of that process as it moved from one of customer acceptance testing, to joint verification, and finally to joint design and development. The focus of this paper will be the impact of this Joint Development process on the quality of the DMS-10 software.>