structural:expansion, information:filtering
Relation to other branches of government

Legislatures vary widely in the amount of political power they wield, compared to other political players such as judiciaries, militaries, and executives. In 2009, political scientists M. Steven Fish and Matthew Kroenig constructed a Parliamentary powers index in an attempt to quantify the different degrees of power among national legislatures. The German Bundestag, the Italian Parliament, and the Mongolian State Great Khural tied for most powerful, while Myanmar's House of Representatives and Somalia's Transitional Federal Assembly (since replaced by the Federal Parliament of Somalia) tied for least powerful.

Some political systems follows the principle of legislative supremacy, which holds that the legislature is the supreme branch of government and cannot be bound by other institutions, such as the judicial branch or a written constitution. Such a system renders the legislature more powerful.

In parliamentary and semi-presidential systems of government, the executive is responsible to the legislature, which may remove it with a vote of no confidence. On the other hand, according to the separation of powers doctrine, the legislature in a presidential system is considered an independent and coequal branch of government along with both the judiciary and the executive. Nevertheless, many presidential systems provide for the impeachment of the executive for criminal or unconstitutional behaviour.

Legislatures will sometimes delegate their legislative power to administrative or executive agencies.