The Legislative Assembly is composed of 57 deputies, (Spanish: diputados), who are elected by direct, universal, popular vote on a closed party list proportional representation basis, by province, for four-year terms.

[9] Deputies cannot accept, after being sworn in, under penalty of losing their credentials, any position or employment in the other Powers of the State or autonomous institutions, except in the case of a Ministry of Government.

From the time they are declared proprietor or alternate deputies, until they end their legal term, they may not be deprived of their liberty for criminal reasons, except when they have previously been suspended by the Legislative Assembly.

It is not possible, according to current legislation, for a citizen to directly run for the position of an independent deputy without the representation of a political party.

No one may be forced to be part of any association.However, as the Supreme Electoral Court of Costa Rica has repeatedly observed,[11][12][13][14][15] since deputies are popularly elected, their nomination must be made through a political party, due to the framework of the current legal system, in which the political parties have a monopoly on the nomination of candidates for deputies according to the Electoral Code.

Several independent deputies through history have asked the Constitutional Chamber of the Supreme Court of Justice of Costa Rica, to be recognized as the head of a parliamentary fraction or to have the financial resources of a parliamentary fraction, in contradiction with the regulations, this court has stated:[16][17][18] Indeed, it is not possible under any circumstances, to claim that any deputy who separates from the Fraction to which he belongs, is declared as a new Political Fraction, with all the attributions and duties inherent to this condition, both due to the existence of a regulatory provision that defines and restricts the concept of "Parliamentary Fraction", as well as a basic aspect of common sense, which seeks to establish the necessary limits to achieve the ideal organizational mechanisms that allow, in turn, an effective and efficient development of the legislative tasks.The eventual subsequent separation of a deputy from the political party for which he was elected does not mean that the deputy loses his status as such, being that at all times he maintains the powers, rights and duties inherent to his position; But the foregoing does not imply that his separation empowers him to acquire, ex officio and full right, the competences that are typical of a figure expressly provided in the Regulations, with particular duties and rights and intended to be the representative of a group of deputies elected under the same political flag.Thus, there is no regulatory possibility of forming a fraction not linked to the representation of a political party that has elected at least one representative by means of suffrage, understood in accordance with article 93 of the Political Constitution of Costa Rica.

Different experts have recommended the increase in the number of deputies as an urgent need to improve representativeness, but this proposal is highly unpopular among the population and generates rejection reactions.

[23] A report by the United Nations Development Programme and the Center for Research and Political Studies of the University of Costa Rica recommended increasing the number of legislators to 82.

However, since much of the building materials were imported from Germany and Czechoslovakia, the onset of the Second World War put a halt to the project.

[29] The modern assembly was created in the aftermath of the Costa Rican Civil War that deposed Teodoro Picado Michalski in 1948.