The study of complex systems has expanded rapidly in recent decades, driving the development of powerful techniques that can be applied across a wide range of disciplines. The growing philosophical examination of complexity alongside scientific advances offers profound and far-reaching insights. This book delves into the philosophy of complexity, supported by interdisciplinary examples. It opens with a concise introduction to the concepts of stability and information, as well as the necessary mathematical formalism. A range of fascinating topics are then explored, including the nature and meaning of complexity, deterministic chaos, coarse graining, scale invariance, network science, machine learning, and complex mental dynamics. These areas are linked to challenging topics in philosophical discourse, such as interlevel relations, notions of meaning, action and agency, creative insight, and understanding. This text will be of interest to students and researchers studying complex systems across a range of disciplines, from physics to cognitive science.