Spain uses the system of male-preference cognatic primogeniture. Dynasts who marry against the express prohibition of the monarch and the Cortes are excluded from the succession together with their descendants. A prohibition expressed only by the monarch or only by the Cortes will have no consequences to the succession. Disputes about the succession are to be settled by legislation.
Upon succeeding to the throne, the monarch is required by article 61(1) of the 1978 constitution to take an oath on the occasion of his being proclaimed before the Cortes Generales.
The historical list of potential successors with dynastic rights was much longer, but the Spanish Constitution of 1978 (art. 57.1) limits the line of succession to descendants of King Juan Carlos I.
Section 1 of Article 57 of the Spanish Constitution of 1978 provides that "The Crown of Spain shall be inherited by the successors of H. M. Juan Carlos I de Borbón." To date, no clarification has been made whether this provision includes anyone beyond the descendants of King Juan Carlos: "Successors" may not be presumed to be synonymous with "descendants".
King Juan Carlos's two sisters renounced their rights of succession, but those renunciations took place before the adoption of the Constitution. The rights of earlier generations are similarly clouded by numerous renunciations and unapproved marriages which may or may not exclude the individuals involved from the throne.
Article 57 further provides that "Abdications and renunciations and any doubt in fact or in law that may arise in connection with the succession to the Crown shall be settled by an organic act." Article 57 further states that "Should all the lines designated by law become extinct, the Cortes Generales shall provide for succession to the Crown in the manner most suitable for the interests of Spain."
Unless and until an organic act clarifies the rights of other members of the King's family, it is unknown who, if anyone, follows Infanta Cristina's descendants in the line of succession.
In its 2004 election manifesto, the victorious Spanish Socialist Workers' Party (PSOE) included plans to adopt absolute primogeniture, a proposal which was supported by the leader of the main opposition party, the conservative People's Party. It was initially thought that the change would only apply to future generations but with all the major political parties in agreement that the system of male-preference primogeniture conflicts with the constitutionally established principle of gender equality, it was planned that the law would be changed before the Princess of Asturias bore a son, thereby demoting Infanta Leonor in the line succession. The subsequent announcement, in 2006, that the Princess was pregnant with a second daughter, however, removed any immediate urgency in the passage of the necessary legislation.