Niklas Luhmann was a prominent German sociologist and social theorist, particularly renowned for his distinctive brand of systems theory. A writer of over 70 books, he applied his systems-theoretical perspective to subjects as diverse as law, economics, mass media and love. His Introduction to Systems Theory (Polity, 2012) is a foundational text, providing a clear overview of concepts and their relation to almost all aspects of society. Luhmann was professor of sociology at the University of Bielefeld until his retirement in 1993, when he was finally able to complete his magnum opus, Theory of Society (1997). His theories continue to be of great relevance, informing work in a whole range of fields including cognitive science, ecology, and the study of social movements. Apart from Introduction to Systems Theory, Polity has published numerous books by Luhmann including The Reality of the Mass Media, Love as Passion and Love: A Sketch.