The Spanish Cortes Generales were envisaged as an imperfect bicameral system. The Congress of Deputies had greater legislative power than the Senate, having the ability to vote confidence in or withdraw it from a Prime Minister and to override Senate vetoes by an absolute majority of votes. Nonetheless, the Senate possessed a few exclusive, yet limited in number functions—such as its role in constitutional amendment—which were not subject to the Congress' override. Voting for the Cortes Generales was on the basis of universal suffrage, which comprised all nationals over eighteen and in full enjoyment of their political rights. For the Congress of Deputies, 348 seats were elected using the D'Hondt method and a closed list proportional representation, with a threshold of 3 percent of valid votes—which included blank ballots—being applied in each constituency. Parties not reaching the threshold were not taken into consideration for seat distribution. Additionally, the use of the D'Hondt method might result in an effective threshold over three percent, depending on the district magnitude. Seats were allocated to constituencies, corresponding to the provinces of Spain. Each constituency was entitled to an initial minimum of two seats, with the remaining 248 fixed among the constituencies in proportion to their populations, at a rate of approximately one seat per each 144,500 inhabitants or fraction greater than 70,000. Ceuta and Melilla were allocated the two remaining seats, which were elected using plurality voting. For the Senate, 208 seats were elected using an open listpartial block voting, with electors voting for individual candidates instead of parties. In constituencies electing four seats, electors could vote for up to three candidates; in those with two or three seats, for up to two candidates; and for one candidate in single-member districts. Each of the 47 peninsular provinces was allocated four seats, whereas for insular provinces, such as the Balearic and Canary Islands, districts were the islands themselves, with the larger—Majorca, Gran Canaria and Tenerife—being allocated three seats each, and the smaller—Menorca, Ibiza–Formentera, Fuerteventura, La Gomera, El Hierro, Lanzarote and La Palma—one each. Ceuta and Melilla elected two seats each. The law also provided for by-elections to fill seats vacated up to two years into the legislature. Additionally, autonomous communities could appoint at least one senator each and were entitled to one additional senator per each million inhabitants. The electoral law provided that parties, federations, coalitions and groupings of electors were allowed to present lists of candidates. However, groupings of electors were required to secure the signature of at least 0.1 percent of the electors registered in the constituency for which they sought election—needing to secure, in any case, the signature of 500 electors—. Electors were barred from signing for more than one list of candidates. Concurrently, parties and federations intending to enter in coalition to take part jointly at an election were required to inform the relevant Electoral Commission within fifteen days of the election being called.
Election date
The term of the Cortes elected in the 1977 election was not to be continued beyond 15 June 1981 in the event they were not dissolved earlier. An election was required to be held within from thirty to sixty days after the date of expiry of the Cortes Generales, setting the latest possible election date for the Cortes Generales on Friday, 14 August 1981. The Prime Minister had the prerogative to dissolve both Houses at any given time—either jointly or separately—and call a snap election, provided that no motion of no confidence was in process, no state of emergency was in force and that dissolution did not occur before one year had elapsed since the previous one. Additionally, both Houses were to be dissolved and a new election called if an investiture process failed to elect a Prime Minister within a two-month period from the first ballot.
Parties and leaders
Below is a list of the main parties and coalitions which contested the election:
Opinion polls
Voting intention estimates
The table below lists voting intention estimates in reverse chronological order, showing the most recent first and using the dates when the survey fieldwork was done, as opposed to the date of publication. Where the fieldwork dates are unknown, the date of publication is given instead. The highest percentage figure in each polling survey is displayed with its background shaded in the leading party's colour. If a tie ensues, this is applied to the figures with the highest percentages. The "Lead" column on the right shows the percentage-point difference between the parties with the highest percentages in a given poll. When available, seat projections are also displayed below the voting estimates in a smaller font. 176 seats were required for an absolute majority in the Congress of Deputies.
Voting preferences
The table below lists raw, unweighted voting preferences.
