A definition of ‘systems engineering’ is proposed, to stimulate further discussion directed towards a concensus view. It is a hybrid methodology comprising three modes: policy analysis, design, and management. Thus it is a matrix of methodologies drawing on the procedures provided by people working in a wide range of functions, which are integrated to constitute a total system. Systems engineering is different from classical engineering. It is the product and the price of that technological progress that leads to ever more complex man-made systems. It breaks through the ‘complexity threshold’ to ensure that major enterprises are properly conceived and successfully brought into being.