Sunday will be a big day in Spain: across the country, citizens will vote for their representatives in Congress. The next prime minister (el presidente del gobierno) will also be chosen, based in part on party representation in Congress.
This year there are four viable national parties instead of only two (other parties will also gain seats in Congress). If one party ends up with a majority of seats in Congress, they will put forth their candidate for prime minister for approval by the king and a subsequent vote of confidence by Congress. If no party attains majority status—which is what is expected to happen this time around—then the parties with the greatest representation in Congress will negotiate to put forward a single candidate and platform.
Although not directly elected*, candidates for prime minister have been touring the country and participating in debates, and they appear as the face of their party in campaign literature. I don’t know enough about Spanish history and politics to understand the important nuances, but what I see are pretty standard pledges to address what the average voter cares about: government spending, jobs and pensions, and access to high quality education and healthcare. I also see jabs at incumbent officials and parties in proposals to fight corruption, and pointed reminders that Spain is a unified, democratic country (a statement against the independence/secessionist movements in two provinces).
*If that sounds odd, it helps to remember that presidential candidates in the U.S. are also selected through a party nomination process and that, because of the electoral college system, we also don’t vote directly for them.