When considering factors that influence a firm's success, topics like strategy, technology, and leadership get significant managerial attention.Yet organization design--the accountability system that defines rights, roles, and responsibilities throughout a firm--is often left to evolve naturally, without conscious planning or oversight.Robert Simons argues that this is a critical mistake that inevitably results in diminished performance and competitiveness over time.I ndeed, organization design impacts the performance of every individual in a firm--from what kind of information employees receive to how they prioritize tasks to how they are held accountable for results. As such, contends Simons, organization design is actually the most important determinant of success for implementing strategy in any large enterprise.