Soria (Congress of Deputies constituency)

The constituency was created as per the Political Reform Law and was first contested in the 1977 general election. The Law provided for the provinces of Spain to be established as multi-member districts in the Congress of Deputies,^[2] with this regulation being maintained under the Spanish Constitution of 1978.^[3] Additionally, the Constitution requires for any modification of the provincial limits to be approved under an organic law, needing an absolute majority in the Cortes Generales.^[4]

Voting is based on universal suffrage, comprising all Spanish nationals over 18 years of age with full political rights, provided that they have not been deprived of the right to vote by a final sentence.^[5] 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.^[6][7] Amendments in 2011 required non-resident citizens to apply for voting, a system known as "begged" voting (Spanish: Voto rogado).^[8][9] which was abolished in 2022.^[10] Further, amendments in 2018 granted the right to vote to those legally incapacitated.^[11] The Congress of Deputies has a minimum of 300 and a maximum of 400 seats, with electoral provisions fixing its size at 350. Of these, 348 are elected in 50 multi-member constituencies corresponding to the provinces of Spain—each of which is assigned an initial minimum of two seats and the remaining 248 distributed in proportion to population—using the D'Hondt method and closed-list proportional voting, with a three percent-threshold of valid votes (including blank ballots) in each constituency. The remaining two seats are allocated to Ceuta and Melilla as single-member districts elected by plurality voting.^[12] The use of this electoral method may result in a higher effective threshold depending on district magnitude and vote distribution.^[13] The law does not provide for by-elections to fill vacant seats; instead, any vacancies arising after the proclamation of candidates and during the legislative term are filled by the next candidates on the party lists or, when required, by designated substitutes.^[14]

The electoral law allows for parties and federations registered in the interior ministry, alliances and groupings of electors to present lists of candidates. Parties and federations intending to form an alliance are required to inform the relevant electoral commission within 10 days of the election call—15 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. Also since 2011, parties, federations or alliances 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.^[15] Amendments in 2007 required a balanced composition of men and women in the electoral lists, so that candidates of either sex made up at least 40 percent of the total composition; further amendments in 2024 required the use of a zipper system.^[16]