[1] The congress was initially due for 2015, but the various elections held in Spain that year (local, regional and general) and the deadlock in the government formation negotiations leading up to the 2016 general election, as well as a major crisis over the issue within the opposition Spanish Socialist Workers' Party (PSOE), saw the event being delayed until early 2017.

[12] The two-year delay in the congress's calling was brought to the courts by a party member, with the Supreme Court of Spain ruling it as unlawful in December 2020, as it "violated the plaintiff's right of association, in its aspect of the right of democratic participation in the party".

Extraordinary congresses had to be called by a two-thirds majority of the Board of Directors at least one-and-a-half month in advance of their celebration, though in cases of "exceptional urgency" this deadline could be reduced to 30 days.

Note that the Canary Islands use WET (UTC+0) instead):[15] The individuals in this section were the subject of speculation about their possible candidacy, but publicly denied or recanted interest in running: Poll results are listed in the tables below in reverse chronological order, showing the most recent first, and using the date the survey's fieldwork was done, as opposed to the date of publication.

The highest percentage figure in each polling survey is displayed in bold, and the background shaded in the candidate's colour.