AP® Comparative Government and Politics · Unit 2 · Topic 2.6
Unicameral and Bicameral Legislatures
A unicameral legislature has one lawmaking chamber; a bicameral legislature has two, each usually chosen differently, which gives the second chamber a real chance to amend, delay, or block what the first chamber passes.
Countries split lawmaking into two chambers for the same reason a house has two locks: redundancy slows down mistakes and bad-faith entries alike. A second chamber is often built on a different logic than the first, elected from different districts, chosen for longer or staggered terms, or meant to represent regions or elites rather than raw population. That difference in design is the whole point. If both chambers were elected the same way at the same time, the second one would just be an expensive echo.
The mechanism is straightforward: a bill cannot become law until both chambers agree on identical text, so the upper chamber gets to read, amend, delay, or reject what the lower chamber sends up. In federal systems the upper chamber often represents states or regions, so it can block legislation that one party's majority in the lower chamber would otherwise push through unchecked. When the two chambers are controlled by different parties, this stops being a formality. A bill the governing party rams through the lower chamber can sit for months in the upper chamber, get rewritten in committee, or die outright, forcing negotiation that a single chamber would never require.
Across the six course countries, the United Kingdom and Russia are bicameral, with the UK's House of Commons and House of Lords and Russia's Duma and Federation Council. Mexico is bicameral too, with a Senate and Chamber of Deputies. China's National People's Congress, Iran's Majlis, and Nigeria's National Assembly show the range at the other end: China and Iran are unicameral, while Nigeria is bicameral with a Senate and House of Representatives, proving chamber count tracks each constitution's design choices, not some universal rule about development or democracy.
Key terms
- Unicameral
- A legislature with a single chamber that holds full lawmaking power.
- Bicameral
- A legislature split into two chambers, both of which must usually approve a bill for it to become law.
- Upper chamber
- The second chamber in a bicameral system, often chosen differently and meant to represent regions, states, or elites.
- Divided chamber control
- A situation where different parties hold majorities in each chamber, making compromise necessary to pass legislation.
Watch it explained
- How it worksHow does a second chamber slow, amend, or block what the first chamber sends up?
- Going furtherWhat happens to lawmaking when the two chambers are controlled by different parties?
- Worked exampleShow me which of the six course countries have one chamber and which have two.
- Common mistakeWhy isn't a unicameral legislature automatically less democratic than a bicameral one?
Check yourself
End of topic.