Primary care is under the microscope in Canada and worldwide. Governments are spending millions of dollars on reform initiatives to see whether innovative approaches will make any difference to the quality and cost of delivering primary care. The question of where to start in planning the evaluation of a reform is a common concern. This article considers the strengths and weaknesses of logic models in helping to evaluate reforms and highlights the model for the Nova Scotia Primary Care Demonstration Project evaluation. Lessons learned from the development of a logic model for this project are also discussed.