LI Legislature of the Mexican Congress

The LI Legislature of the Congress of the Union (LI Legislatura del Congreso de la Unión) was the 51st session of the Congress of Mexico. It sat from 1 September 1979 to 31 August 1982.

The session's senators had been elected in the 1976 general election while the deputies were elected in the 1979 legislative election.

This congressional session marked a watershed in that it was the first held under the 1977 political reforms whereby several parties on the left and the right obtained official registration and with which access to Congress by opposition parties (i.e. those other than the hegemonic Institutional Revolutionary Party) was made much more viable. The session's members included the first deputies from the Mexican Communist Party (PCM), the Workers' Socialist Party (PST) and the Mexican Democratic Party (PDM). The reforms also increased the number of deputies: 300 from single-member constituencies and 100 from regional lists.

Senate
The 1976 general election had elected two senators for each state and the Federal District – a total of 64 – to serve six-year terms. They were in office for the 50th and 51st sessions of Congress (1976–1982).

President of the Senate

 * 1976–1982: Joaquín Gamboa Pascoe PRI Party (Mexico).svg

Chamber of Deputies
The 51st Congress was elected in the July 1979 mid-term election following the 1977 political reforms: the number of single-member constituencies was increased to 300 (from 196 in the 50th Congress), the proportional representation system was expanded to 100 seats (compared to 41 in the 50th Congress), and three parties obtained their first deputies: the Mexican Communist Party (PCM), the Workers' Socialist Party (PST) and the Mexican Democratic Party (PDM).

Proportional representation deputies
For the 1979 election, 100 proportional representation deputies were elected from three electoral regions.