This chapter considers why collective action – that is, action involving co-operation between individuals or groups – has to be promoted by the state and how this is done by governments making policy decisions about what action to undertake. It explores the different concerns of the three main social sciences: sociology, economics and politics. Governments are formed by political parties which produce rival policy programmes published at election time. In the extreme case, policies may not change at all, leading to total ‘policy inertia’. The chapter focuses on the need for collective action and for states to promote and deliver it in the shape of policies. Government decisions about what public goods and services to provide and how to provide them are recorded as state laws and policies to guide the actions of the state and other bodies and the behaviour of individual citizens.