Cite as:

Y. Bar-Yam, General Features of Complex Systems, Encyclopedia of Life Support Systems (EOLSS UNESCO Publishers, Oxford, UK, 2002).


From biochemical reactions to global development, complexity has arisen as a unifying feature of our world. In this arena of complex systems, new approaches are central to advancing our understanding and capabilities. These approaches include recognizing the importance of patterns of behavior; the space of possibilities; and adaptive processes that select effective behaviors for a complex world. As a discipline, complex systems is a new field of science studying how parts of a system and their relationships give rise to the collective behaviors of the system, and how the system interrelates with its environment. Social systems formed (in part) out of people, the brain formed out of neurons, molecules formed out of atoms, the weather formed out of air flows are all examples of complex systems. The field of complex systems cuts across all traditional disciplines of science, as well as engineering, medicine and management.

The excitement of scientists as well as the public about this new field reflects its potential impact on our ability to understand questions that affect everyday life, perspectives on the world around us, fundamental philosophical disputes, and issues of public concern including major societal challenges, the dynamics of social networks, the Internet and the World Wide Web, biomedical concerns, psychology, ecology and global development.

In this article we introduce concepts and key insights that guide our understanding of complex systems. We explain these concepts using simple discussions of fads, panics and cliques, and how memory and creativity works. We describe the interplay of collaboration and competition, and the origin of altruism and selfishness. We discuss the role of control in human organizations and how the growing complexity of human civilization is accompanied by a shift from central to distributed control leading to a transition no less important than the industrial revolution.