In this chapter reference will be made in passing to the nature and extent of the critique which has developed recently regarding the types of planning based on the unitary framework of assumptions before moving on to an analysis of the theoretical sources of the atomistic alternative. It will be argued that the latter lies in the domain of neo-classical or marginalist economic theory and some general points of contention about that paradigm will be drawn out. In the last section it will be shown first, that marginalist assumptions occur in various planning theories; second, that these theories are subject to heightened forms of the problems of the basic economic theory; and thirdly that, far from supplying a value-free, positivistic exemplar for theories of planning, marginalism is a particular normative ideal which has difficulties of operationalization even for markets, but whose practicability is severely prejudiced in the context of public-sector decision-making.