Fast-moving social enterprises, strapped for cash and time, face a conundrum when it comes to measuring social performance. Traditional measurement tools, whether inherited from international development or impact investing, don’t make sense. They are either too costly because they were designed for large-scale aid projects or focus on typical business metrics that don’t get to the heart of impact. Lean DataSM applies lean experimentation principles to the collection and use of social performance data. It involves a shift in mindset away from reporting and compliance and toward creating value for a company and its customers.