Web Science is the emergent science of the people, organizations, applications, and of policies that shape and are shaped by the Web, the largest informational artifact constructed by humans in history. Web Science embraces the study of the Web as a vast universal information network of people and communities. As such, Web Science includes the study of social networks whose work, expression, and play take place on the Web. The social sciences and computational sciences meet in Web Science and complement one another: Studying human behavior and social interaction contributes to our understanding of the Web, while Web data is transforming how social science is conducted. The Web presents us with a great opportunity as well as an obligation: If we are to ensure the Web benefits humanity we must do our best to understand it.