This book examines the definition of complexity and its meaning, and its components relative to simple and complicated problems - from a project portfolio perspective and in engineering terms. It investigates its origins in terms of complex adaptive systems and compares the influences on the business world to those of systems observed in the natural world. It examines how systems theory can be used to gain a better understanding of the increasingly complex environment within which a modern portfolio exists. The book navigates through complexity by using tested engineering approaches to ensure a portfolio continues to maximize return.