Continuous software process improvement (SPI) practices have been extensively prescribed to improve performance of software projects. However, SPI implementation mechanisms have received little scholarly attention, especially in the context of distributed software product development. We took an action research approach to study the SPI journey of a large multinational enterprise that adopted a distributed product development strategy. We describe the interventions and action research cycles enacted over a period of five years in collaboration with the firm, which resulted in a custom SPI framework that catered to both the social and technical needs of the firm's distributed teams. Institutionalizing the process maturity framework got stalled initially because the SPI initiatives were perceived by product line managers as a mechanism for exercising wider controls by the firm's top management. The implementation mechanism was subsequently altered to co-opt product line managers, which contributed to a wider adoption of the SPI framework. Insights that emerge from our analysis of the firm's SPI journey pertain to the integration of the technical and social views of software development, preserving process diversity through the use of a multi-tiered, non-blueprint approach to SPI, the linkage between key process areas and project control modes, and the role of SPI in aiding organizational learning.