Public choice seeks to understand and predict the behaviour of politicians and bureaucrats in the polity by utilising analytical techniques developed from economics, based on the postulate of rational choice. In other words, public choice is an application of neoclassical economic tools (self interest and utility maximisation) to explain political behaviour.
In public choice, individuals, interest groups, bureaucrats, and politicians are assumed to seek their own self interest as in the market place. Decisions made depend on the costs and benefits of an action taken whereby each group attempts to maximise their own net benefits. Benefits can take the form of monetary or non-monetary rewards and can includes ideologies, goals, and cultural values.
The seeking of self interest by bureaucrats and politicians, and collective action by the various interest groups in turn result in the adoption of a particular stance in the specification of institutions and property rights. Excellent discussions of public choice theory can be found in Libecap (1989), Mueller (1989), Rowley (1995) and Wills (1997) in my selected bibliography.