Pedro Sánchez, the leader of the Socialist Party (PSOE), casts his vote in a cultural center in Pozuelo de Alarcón in Madrid.

Pablo Casado, the leader of the conservative Popular Party (PP), casts his vote in a polling station in Madrid.

Pablo Iglesias, the leader of the anti-austerity Unidas Podemos party, casts his vote in the Galapagar municipality in Madrid.

Santiago Abascal, the leader of the far-right party Vox, casts his vote in a polling station in the center of Madrid.

Íñigo Errejón, the candidate for Más País, votes at a school in Madrid.

Albert Rivera, the leader of the center-right Ciudadanos (Citizens), casts his vote in a cultural center in Pozuelo de Alarcón in Madrid.

Polling station in Vaixell Burriac de Vilassar de Mar college (Barcelona). In this image, Quim Ferrer, from the Catalan European Democratic Party (PDeCAT) and ex-mayor of the town, casts his vote.

Voters line up at midday to cast their vote at the Terrassa Municipal Music School in Barcelona province.

Most of the polling stations opened their doors at 9am. Around 37 million Spaniards have the right to vote in this election. In this image, a citizen casts his ballot at a polling station in Alcalá de Henares (Madrid).

Near the polling station in the University of Barcelona, a sign in Catalan reads: “Free them all,” in reference to the Catalan leaders sentenced by the Spanish Supreme Court to prison for their involvement in the 2017 breakaway bid. The Supreme Court sentence, which was announced in October, led to week-long violent street protests in Barcelona.

Polling station in Pinar del Rey in Madrid.

Polling station in the University of Barcelona on Sunday.

Citizens vote at the Sortidor civic center in Barcelona’s Poble Sec neighborhood.

Two nuns vote at a polling station in Madrid.

Polling station in Montecarmelo, Madrid.

Pascual Huguet casts his vote in the Sortidor civic center in Barcelona with a sign that says: "I’m gonna vote, don’t hit me." Huguet says his son was beaten up by police when he went to vote in the unauthorized referendum on Catalan independence on October 1, 2017.

Polling station in Pavelló de Palau in Girona.

A police officer from the Catalan regional police force, the Mossos D'Esquadra, patrols the entrance of the polling station at the University of Barcelona.

Election officials are paid for their work at a polling station in a school in the San Agustín neighborhood in Madrid.