Complexity is the science of complex systems

“A system is complex, in the sense that a great many independent agents are interacting with each other in a great many ways.”
M. Waldorp, Complexity, Viking 1993.

“The complex whole may exhibit properties that are not readily explained by understanding its parts. The complex whole, in a completely nonmystical sense, can often exhibit collective properties, “emergent” features that are lawful in their own right.”
S. Kaufmann, At Home in the Universe, Oxford University Press 1996.

“You generally find that the basic components and the basic laws are quite simple; the complexity arises because you have a great many of these simple components interacting simultaneously. The complexity is actually in the organization—the myriad possible ways that the components of the system can interact.”
S. Wolfram

“The task of formulating theory for CAS [complex adaptive system] is more than usually difficult because the behaviour of a whole CAS is more than a simple sum of the behaviours of its parts; CAS abound in nonlinearities”
J. H. Holland, Emergence, Perseus 1999.

“To understand the behavior of a complex system we must understand not only the behaviour of the parts but how they act together to form the whole.”
Y. Bar-Yam, Dynamics of Complex Systems, Addison-Wesley 1997.

“Complexity is not located at a specific, identifiable site in a system. Because complexity results from the interaction between the components of a system, complexity is manifested at the level of the system itself. There is neither something at a level below (a source), nor at a level above (a meta-description), capable of capturing the essence of complexity.
P. Cilliers, Complexity and Postmodernism, Routledge 1998.

"Every PhD student in everything should get to grips with the ‘chaos/complexity’ programme, not for reasons of fashion or even legitimate career building, but because this is the way the world works and we need to understand that"
D. Byrne, Complexity and the Social Sciences, Routledge 1998).

“Complexity is not a methodology or a set of tools (although it does provide both). It certainly is not a management fad. The Science of Complexity provides a conceptual framework, a way of thinking, a way of seeing the World"
E. Mitleton-Kelly

“I think the next century will be the century of complexity”
S. Hawking