Real Academia Espaņola (RAE) ("Royal Spanish Academy") is the institution that regulates the Spanish language. It is based in Madrid, Spain, but has affiliations with national language academies in 21 Spanish-speaking nations.
The RAE has as a goal the preservation and continuity of the Spanish language, and as such is considered conservative. One description of its aims is "to assure that Spanish speakers will always be able to read Cervantes," but it also exercises a progressive influence in keeping the formal language up-to-date. For instance in 1994 it ruled that the Spanish consonants ch and ll would be alphabetized normally, and not separately as in the past.
The Academy also watches small details, such as adding an accent in 1959 to the pronunciation of forms of reunir to assure that the eu was not taken as a diphthong.
This careful, scholarly approach is in sharp contrast to the wide-open style of the English language.
The RAE has a formal procedure for "admitting" words to the Spanish language and is a major publisher of dictionaries and grammars. Its web site includes an on-line dictionary and many other resources, all in Spanish.