The term complexity is often loosely appropriated by both academics and practitioners to describe things that lack simple explanations. However, little conceptual clarity exists regarding the meaning of the term. This is partly due to the diverse history of complexity theory, which evolved from the interplay of several disciplines. In this chapter, a partial account of this history is offered. To this end, an overview of first-order cybernetics and information theory, second-order cybernetics and autopoiesis, third-order cybernetics and artificial life, and General Systems Theory is presented. The influence of these theoretical predecessors on philosophical complexity is highlighted, as are the central points of divergence. In so doing, a description of the features of philosophical complexity emerges. Apart from its heterogeneous history, complexity theory currently refers to a number of theoretical enterprises, based on different assumptions, methodologies, and aims. In this chapter, philosophical complexity is also compared and contrasted with the scientific school of complexity theory. The goal is to illustrate why philosophical complexity—which can best be described as presenting a particular view of ontology, rather than a theory of causation—necessitates a different methodological approach to that of scientific complexity.