Software project telemetry is a new approach to software project management in which sensors are attached to development environment tools to unobtrusively monitor the development process and products. This sensor data is abstracted into high-level perspectives on development trends called telemetry reports, which give project members useful insights for local, in-process decision making. This article presents software project telemetry's essential characteristics, contrasts it to other approaches such as predictive models based upon historical software project data, describes a reference framework implementation called Hackystat, and presents the authors' lessons learned so far.