Forty thousand years ago, humans discovered the main key to progress: cooperation. They became the wisest of primates when they learned to make agreements among themselves. Collaborating so that everyone could develop and realize their life plans is a distinctly human form of organization. Had humans been solitary creatures, no matter how intelligent or strong, none could have achieved a fraction of what an average person accomplishes within a cooperative framework. We live our lives focused on short-, medium-, and long-term projects, striving to achieve them, yet often overlook that our success depends on the contributions of millions of people we will never meet. Collaboration is central to the design and realization of life plans; so central, in fact, that an adequate conception of freedom as applying to the social world should include the dimension of cooperation.