Congress of the Union (Mexico)

Composition and electoral system

The full membership of the Congress totals 628 representatives: 128 senators and 500 deputies. The Senate, or upper chamber, represents the federative entities and is made up under a mixed system combining state-level seats with national proportional allocation; senators commonly serve terms aligned with the presidential term. The Chamber of Deputies, the lower house, combines single-member districts with party-list proportional representation to reflect both local and national voting patterns.

Powers and functions

Both chambers share responsibility for the enactment and amendment of federal law, but each has specific duties assigned by the constitution. Typical functions include:

• Drafting and passing federal legislation and constitutional amendments.
• Approving the federal budget and overseeing public expenditure.
• Reviewing and ratifying certain presidential appointments and international treaties.
• Exercising oversight of the executive through inquiries, commissions and other parliamentary mechanisms.

History and institutional development

Mexico's bicameral legislature has roots in 19th-century constitutional design and has evolved alongside the country's political changes. Across the 20th and early 21st centuries, electoral reforms altered representation rules, candidate eligibility and re-election practices to increase competitiveness and strengthen legislative accountability. These changes have shaped how parties, federal entities and voters interact within the congressional system.

Operations, locations and notable facts

Congressional business is carried out through plenary sessions and a system of standing committees that examine proposals in detail before floor debate. The two chambers maintain separate meeting places and administrative structures but must coordinate on joint procedures for certain acts, such as constitutional reforms. The upper body is commonly referred to as the Senate of the Republic (Senate), while the lower house is known as the Chamber of Deputies (Deputies). Both meet in Mexico City (seat of government).

Importance and distinctions

The Congress of the Union plays a central role in Mexico’s democratic governance: it enacts the legal framework for the country, approves public finances, and provides checks on the executive. Distinctions between the two chambers — representation by federal entities in the Senate versus population-based representation in the Chamber of Deputies — reflect the dual goals of protecting regional interests while giving weight to population distribution in national policy-making.