In response to the New York City’s near bankruptcy in the mid-1970s, the Planning, Management and Reporting system was enshrined the City Charter.  This comprehensive approach to data-driven decision making, which laid the foundation for the modern performance management movement, has functioned through five city administrations. The most visible part of the system, the Mayor’s Management Report (MMR), is issued twice a year, reporting on the performance of city agencies. The evolution of this performance management approach, the longest running and most transparent of any large city in the country, has received little scholarly attention. This study, by an early student of performance measurement and management and by the current deputy director for performance management in the Mayor’s Office, traces how the MMR has evolved over the years to influence the management of the country’s largest city, assessing both the progress and the problems of metrics in complex public management systems.