During the 10th Legislature, the Senate has a total of 266 Senatores, elected by a dual procedure:

• a) Most of them (208) are elected by provinces; each province elects four Senators, by universal suffrage in a free, equal, direct and secret vote (section 69.2 SC and 165.1 LOREG). In the insular provinces, each island or group of islands with a "Cabildo" or insular Council constitutes an electoral district for the purpose of election of Senators. Each of the larger islands (Gran Canaria, Mallorca and Tenerife) elects three Senators and each of the smaller islands or groups of islands (Ibiza-Formentera, Menorca, Fuerteventura, Gomera, Hierro, Lanzarote and La Palma) elects one Senator (section 69.3 SC and 165.2 LOREG). Ceuta and Melilla elect two Senators each (section 69.4 SC and 165.3 LOREG). Electors may cast their votes to a maximum of three candidates in the peninsula provinces, to two in Gran Canaria, Mallorca, Tenerife, Ceuta and Melilla, and to one in the smaller islands. Those obtaining more votes are elected (section 166 LOREG).
  
  
• b) Furthermore, each Self-governing Community appoints one Senator, and an additional Senator for every million inhabitants in their respective territories. This appointment is made by the legislative Assembly or, failing this, by the supreme body of government of the Self-governing Community, in accordance with the provisions of the respective Statutes which shall ensure, in all cases, appropriate proportional representation (section 69.5 SC and 165.4 LOREG). The official population census in effect when the last elections to the Senate were held shall serve as the basis for determination of the specific number of Senators that correspond to each Self-governing Community. The official population census in effect when the last elections to the Senate were held shall serve as the basis for determination of the specific number of Senators that correspond to each Self-governing Community. At present, the total number of Senators appointed by the Self-governing Communities is 58, pursuant to the agreement adopted by the Permanent Deputation of the Senate during its sitting held on 28 September 2011.

Appointment of these Senators is contemplated as a secondary degree election, in which the only requisite established in the Constitution is that appropriate proportional representation be guaranteed. Each Self-governing Community regulates the electoral procedure in its Statute, Self-governing Act of Standing Orders of the House. The following requisites -that are not required in all Self-governing Communities- may be highlighted:

1. Membership of the regional Parliament making the appointment.
2. Membership of the Self-governing Community.
3. Proposal as candidate.
4. Declaration of acceptance of the position.

The evolution of the number of Senators appointed by each Self-governing Community since the 1st. Legislature is refected in the following table: [PDF]