[3] Additionally, the Constitution requires for any modification of the provincial limits to be approved under an organic law, needing an absolute majority in the Cortes Generales.

[4] Voting is on the basis of universal suffrage, which comprises all nationals over 18 years of age and in full enjoyment of their political rights.

[5] The only exception was in 1977, when this was limited to nationals over 21 years of age and in full enjoyment of their political and civil rights.

Each of the 47 peninsular provinces is allocated four seats, whereas for insular provinces, such as the Balearic and Canary Islands, districts are the islands themselves, with the larger—Mallorca, Gran Canaria and Tenerife—being allocated three seats each, and the smaller—Menorca, Ibiza–Formentera, Fuerteventura, La Gomera and El Hierro (which comprised a single constituency only for the 1977 election), Lanzarote and La Palma—one each.

Also since 2011, parties, federations or coalitions that have not obtained a mandate in either chamber of the Cortes at the preceding election are required to secure the signature of at least 0.1 percent of electors in the aforementioned constituencies.