When a marketplace is considered in isolation, the implicit conclusion is that markets are a sufficient defence against the exercise of power. But market transactions do not occur in isolation: they are defined by rules, property rights, prior events and social values. This book widens the focus of traditional economic analysis to examine the ways in which people may affect each other within and around markets to give rise to real power. Using conventional neoclassical assumptions about human behaviour, the book begins by developing a workable concept of power, allowing for its presence in a variety of forms and degrees. It examines the conditions under which power would necessarily be absent from market transactions and those under which it would be possible. It considers the decision processes of potential exercisers and subjects of power to determine when the exercise and success of power would be rational.