Spain

Article 3.1 states:

The following persons cannot vote…

• (b) those who are declared incompetent by a Court of Law - provided that they are explicitly declared incapable of voting,
• (c) the inmates of psychiatric wards placed there by judicial decree and explicitly declared by a judge incapable of voting…

Article 87 states:

Those voters who cannot read or who, being disabled, cannot take the ballot paper or place it inside the envelope and hand it to the President of the Polling Station, can be assisted, to undertake these actions, by a person they rely on.

Article 150.1 states:

The public powers that according to their legal competences call an electoral process can carry out during the electoral period an institutional campaign oriented to inform citizens about: the election day, the voting procedure and the requirements and procedure for postal voting, without influencing, in any case, orientation of vote of the electors. This institutional publicity will be carried out in free spaces of the public media of the geographical region corresponding to the electoral process, with enough extent to reach the aims of this campaigns.
 

Article 164.1 states:

In the case of death, disability, or resignation of a deputy, the seat will be given to the candidate, or, where appropriate, to the substitute from the corresponding list, according to the order of placement.

Article 166.2 states:

In the case of death, disability, or resignation of a Senator who was directly elected, the vacancy will be covered by his or her substitute designated according to Article 171 of this law.

Article 182.1 states:

In the case of death, disability, or resignation of a councilor, the seat will be given to the candidate, or, where appropriate, to the substitute from the corresponding list, according to the order of placement.

Article 184, part (f) states:

In the case of death, disability, or resignation of a councilor, the vacancy will be given to the candidate who secured the next highest number of votes.

Article 208.1 states:

In the case of death, disability, resignation, or loss of status of the Councillor of a Provincial Deputy, his or her vacancy will be occupied by one of the elected substitutes in the corresponding judicial district according to the established order among them.

Article 217 states:

In the case of death, disability, or resignation of a deputy of the European Parliament, the seat will be given to the candidate, or, where appropriate, to the substitute from the corresponding list, according to the order of placement.

Excerpts from the Organic Law on the Regime of General Elections (1987, last amended 2007)

Section 59, subsection 2 states:

If the King becomes unfit for the exercise of his authority, and this incapacity is recognized by the Cortes Generales, the Crown Prince shall immediately assume the Regency…

Excerpt from the Constitution of the Kingdom of Spain (1978, last amended 2018)