The Doctors Company (TDC), the largest national insurer of physician and surgeon medical liability in the US, provides lessons on how to use business rules platforms and Lean development to raise the pace of application delivery. At the same time, TDC has been replacing its legacy systems with a modern, new generation. TDC turned to business rules as a key part of a new IT architecture and development process that values responsiveness to business demands first. Application development professionals can learn from TDC's best practices, which are to: 1) target rules at fast-changing decisions; 2) employ integrated project teams and prototyping; 3) manage rules centrally but execute them locally; and 4) invest in a strong design foundation.