It can be cognitively demanding to understand how a system or organization made up of many very different interconnected elements actually works. But the fact that such systems or organizations are difficult to understand doesn’t make them inherently bad. In addition to its more obvious costs, complexity confers critical benefits, especially in dynamic and uncertain environments. The authors draw on their experience and perspectives in business, biology, and physics to offer some reflections on the nature, benefits, and costs of complexity and provide some guidance on managing it. Their recommendations: In growing your organization, make sure that it remains modular in structure and that all components and connections conform to a small number of simple operating principles. Embed a bias for change, avoid imposing too many controls on your people, and let the market judge which changes work. Finally, always optimize your organization globally and keep fixing, repairing, and pruning.