Entity consisting of many diverse and autonomous components or parts (called agents) which are interrelated, interdependent, linked through many (dense) interconnections, and behave as a unified whole in learning from experience and in adjusting (not just reacting) to changes in the environment. Each individual agent of a CAS is itself a CAS: a tree, for example, is a CAS within a larger CAS (a forest) which is a CAS in a still larger CAS (an ecosystem). Similarly a member of a group is just one CAS in a chain of several progressively encompassing a community, a society, and a nation. Each agent maintains itself in an environment which it creates through its interactions with other agents. Every CAS is more than the sum of its constituting agents and its behavior and properties cannot be predicted from the behaviors and properties of the agents. CAS are characterized by diffused (distributed) and not centralized control and, unlike rigid (mechanistic) systems, they change in response to the feedback received from their environment to survive and thrive in new situations. In inanimate world many phenomenon behave as CAS, such as fashion trends, stock markets, traffic jams.