The Spanish Socialist Workers' Party (PSOE), in opposition for the first time since 1982, recovered some ground from its previous result.

United Left (IU) lost half of its votes and parliamentary representation amid internal divisions—Initiative for Catalonia (IC) and the New Left (NI) had split from the larger alliance in 1997—policy differences over their relationship with the PSOE and the deteriorating health condition of IU's maverick leader, Julio Anguita.

Voting was on the basis of universal suffrage, which comprised all nationals and resident non-national European citizens over 18 years of age and in full enjoyment of their political rights.

[1] The use of the electoral method resulted in an effective threshold based on the district magnitude and the distribution of votes among candidacies.

In order to be entitled to run, parties, federations, coalitions and groupings of electors needed to secure the signature of at least 15,000 registered electors; this requirement could be lifted and replaced through the signature of at least 50 elected officials—deputies, senators, MEPs or members from the legislative assemblies of autonomous communities or from local city councils.