Constitutional government is a political science term which refers to a government acting within constitutional law and the constitution. The constitutional government is typically clear in countries with a codified constitution, such as the United States (see the Constitution of the United States). Their behaviour is typically either compliant with the state constitution, or not.

In liberal democracies with an uncodified constitution (of which there are three - United Kingdom, New Zealand, and Israel), where there is not a single document and constitutional law is drawn from several sources, the constitutional government is less well defined. To use the United Kingdom as an example, all Acts of Parliament are statute law and hence constitutional - this is due to parliamentary sovereignty. As such, all behaviour of the government that falls within the laws set out by the various sources of the constitution of the United Kingdom is considered constitutional. Of course, due to the fusion of power in the country, the government (executive) is always the majority party of the parliament (legislature) - they can, unless backbench revolt occurs, push for any bill to be passed. Members of parliament normally have aspiration to cabinet and notions of solidarity, hence normally vote along the party line. The fact that the executive can (within reasonable limits) pass whatever statute law they wish, raises issues as to whether government in states lacking a codified constitution are actually constitutional.