From Introduction to General Systems Thinking based on Warren Weaver’s 1948 article “Science and Complexity”
Systems are collections of interrelated things. These things could be mechanical controls, organizations, computers, ideas, processes, social roles, or anything else that can be seen to interact for a purpose or goal. Systems science studies these things and their interrelation in order to derive transdisciplinary insights and deep understanding, often leading to the root causes of problematic phenomena.
The systems thinking that systems science engenders differs from traditional scientific approaches as it provides a framework for studying wholes, instead of parts. Systems thinking is often understood in opposition to Enlightenment reductionist thinking, when, if fact, it should be understood as a complement to it.
Encyclopedia of Complexity and Systems Science by 
Encyclopedia of Systems Biology, E-book by 
Systems Thinkers by 
Conceptual Foundations for Multidisciplinary Thinking by 
Thinking in systems : a primer by 
Systems Thinking for Social Change by 
Systematic by 
An Introduction to General Systems Thinking by 
Non-Equilibrium Social Science and Policy by Systems, Systems Theory, General Systems Theory, Systems Dynamics, Networks, Complexity, Emergence, Resilience, Cybernetics, Information Theory, Entropy, Non-linear Systems, Systems Modeling, and Evolution.
