Biscay is one of the 59 constituencies (Spanish: circunscripciones) represented in the Senate of Spain, the upper chamber of the Spanish parliament, the Cortes Generales. The constituency elects four senators. Its boundaries correspond to those of the Spanish province of Biscay. The electoral system uses an open listpartial block voting, with electors voting for individual candidates instead of parties. Electors can vote for up to three candidates.
Voting is on the basis of universal suffrage, which comprises all nationals over 18 years of age and in full enjoyment of their political rights. The only exception was in 1977, when this was limited to nationals over 21 years of age and in full enjoyment of their political and civil rights. Amendments to the electoral law in 2011 required for Spaniards abroad to apply for voting before being permitted to vote, a system known as "begged" or expat vote (Spanish: Voto rogado), which was abolished in 2022. 208 seats are elected using an open listpartial block voting system, with electors voting for individual candidates instead of parties. In constituencies electing four seats, electors can 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 is allocated four seats, whereas for insular provinces, such as the Balearic and Canary Islands, districts are the islands themselves, with the larger—Mallorca, Gran Canaria and Tenerife—being allocated three seats each, and the smaller—Menorca, Ibiza–Formentera, Fuerteventura, La Gomera and El Hierro (which comprised a single constituency only for the 1977 election), Lanzarote and La Palma—one each. Ceuta and Melilla elect two seats each. Until 1985, the law also provided for by-elections to fill Senate seats vacated up to two years into the legislature.
The electoral law allows for parties and federations registered in the interior ministry, coalitions and groupings of electors to present lists of candidates. Parties and federations intending to form a coalition ahead of an election are required to inform the relevant Electoral Commission within ten days of the election call—fifteen before 1985—whereas groupings of electors need to secure the signature of at least one percent of the electorate in the constituencies for which they seek election—one permille of the electorate, with a compulsory minimum of 500 signatures, until 1985—disallowing electors from signing for more than one list of candidates. Also since 2011, parties, federations or coalitions that have not obtained a mandate in either chamber of the Cortes at the preceding election are required to secure the signature of at least 0.1 percent of electors in the aforementioned constituencies.
^ The percentage of blank ballots is calculated over the official number of valid votes cast, irrespective of the total number of votes shown as a result of adding up the individual results for each party.
