Complex systems physics is a relatively recent branch of modern physics that studies the physical behavior of complex systems such as the economic system (ecophysics) or the climate system assumed as nonlinear and multi-component dynamical systems.

In modern physics a complex system is a multicomponent dynamical system, that is composed of several subsystems that typically interact with each other, describable analytically through mathematical models. This type of system is typically studied through investigations of “holistic” and “reductionist” type, that is through the computation “in toto” of the behavior of subsystems and mutual interactions (possibly non-linear), and not through an analysis of the component taken individually (“the whole is greater than the sum of its parts”).

This global approach is necessary because it is not possible to solve analytically all the components with their interactions, but it is necessary to rely on complex computer simulations to evaluate/analyze the dynamic behavior of each component as well as the mutual interactions that can be described in a simple or linear or non-linear way (see dynamic system). Typical of the complex systems are the concepts of self-organization and emergent behavior. The assumption of complex system embraces therefore most of the real physical systems with many components, compared to the systems considered “simple” in classical physics. Such systems are studied within the framework of complexity theory.