Fusion of powers

Not to be confused with Fusion power.

Fusion of powers is a feature of some forms of government, where some branches of government are integrated or in a hierarchical relationship, instead of separated. In particular, the term is used to describe the relationship of the legislative and executive branches in parliamentary systems, especially the Westminster system.

In the Westminster system, members of the executive must come from the legislature. The system first arose as a result of political evolution in the United Kingdom over many centuries, as the powers of the monarch became constrained by Parliament. The term fusion of powers itself is believed to have been coined by the British constitutional expert Walter Bagehot.

Fusion is contrasted with the separation of powers found in presidential systems and to some degree in semi-presidential governments. Fusion of legislative and executive branches exists in parliamentary democracies by design. In modern democratic polities the judiciary is not fused with either the legislative, or the executive branch.