Feedback Loop is an introduction to the ideas underlying recent experimentation with complexity in architecture. It presents key concepts such as prototyping, non-linear order, emergence, bottom-up thinking, parametric thinking, generative scripting and biomorphism, and it does so in plain language for students of architecture and others who seek an entry point into the discussion of recent design work. Many of these ideas, which arose in other fields of study, are interpreted architecturally, in order to help designers leverage them in the creative act. By showing how the key concepts work together to define a coherent view of architecture, Feedback Loop supports the conclusion that the pursuit of complexity is poised to expand beyond the avant-garde to become a broad-scoped, long-term architectural movement.