What is a Systems Approach?

What is a systems approach? The first step towards answering this question is an understanding of the history of the systems movement, which includes a survey of contemporary systems discourse. In particular, I examine how systems researchers differentiated their contribution from mechanistic science - but also from holistic doctrines; and identify the similarities and sharpest differences between complex systems and other systems approaches. Having set the scene, the second step involves developing a definition of 'system' consistent with the spirit of the systems approach.