The first grammar of the Spanish language (Gramática de la lengua castellana) is presented to Queen Isabella I.

In linguistics, grammar is the set of rules for how a natural language is structured, as demonstrated by its speakers or writers. Grammar rules may concern the use of clauses, phrases, and words. The term may also refer to the study of such rules, a subject that includes phonology, morphology, and syntax, together with phonetics, semantics, and pragmatics. There are, broadly speaking, two different ways to study grammar: traditional grammar and theoretical grammar.

Spanish or Castilian (castellano) is a Romance language of the Indo-European language family that evolved from the Vulgar Latin spoken on the Iberian Peninsula of Europe. Today, it is a global language with 483 million native speakers, mainly in the Americas and Spain, and about 558 million speakers total, including second-language speakers. Spanish is the official language of 20 countries, as well as one of the six official languages of the United Nations. Spanish is the world's second-most spoken native language after Mandarin Chinese; the world's fourth-most spoken language overall after English, Mandarin Chinese, and Hindustani (Hindi-Urdu); and the world's most widely spoken Romance language. The country with the largest population of native speakers is Mexico.

Gramática de la lengua castellana is a book written by Antonio de Nebrija and published in 1492. It was the first work dedicated to the Spanish language and its rules, and the first grammar of a modern European language to be published. When it was presented to Isabella of Castile at Salamanca in the year of its publication, the queen questioned what the merit of such a work might be; Fray Hernando de Talavera, bishop of Avila, answered for the author Nebrija in a letter addressed to the monarch:

After Your Highness has subjected barbarous peoples and nations of varied tongues, with conquest will come the need for them to accept the laws that the conqueror imposes on the conquered, and among them our language; with this work of mine, they will be able to learn it, as we now learn Latin from the Latin Grammar.