The purpose of this chapter has been to set some of the foundational theories for systems thinking and to critically examine the contributions of three leading systems thinkers. I have demonstrated how one thinker, Ludwig von Bertalanffy, can be seen as the father of systems thinking. His notion of a system was visionary. The inadequacy of traditional approaches to the scientific method led him to derive and develop the concept of a system. Peter Senge is another author I have engaged with. Indeed, he is a doyen of the twenty-first century systems thinking. Senge is a proponent of systems thinking not only in relation to its usefulness in the education and development of individuals in personal and professional contexts but also in the study of systems for the sustainability and well-being of communities and societies. He appreciates that everyone has a capacity for systems thinking that can be developed. Systems are of primary importance for still another thinker, Donella Meallows. She has contributed much to the development of systems thinking in the twenty-first century. Meallows has been the anchor of the modern pursuit for sustainability, indicative of the current global concern. Despite the value and potential of systems thinking, it is not without criticisms. Some have argued that systems thinking can be too broad and lacking concrete direction. In the future, many are divided on the trajectory that systems thinking will take. Some argue that it will expand further into interconnected systems, while others argue that reductionism will become a renewed focus with time.