The infinitive (infinitivo) is the base, unconjugated form of the verb. It is a non-finite form which means it only names the action itself, not who performs it or when. Infinitives are the verb forms recorded in dictionaries.

There are three infinitive endings that identify verb classes in Spanish:

Spanish also has special infinitive forms for reflexive verbs, where the pronoun "se" is attached to the end of the regular infinitive form. For example:

Infinitives can be used as nouns, serving as subjects, objects of prepositions, or complements of other verbs.

When used as a subject, the infinitive is treated as singular and masculine. It can be used as the subject of the sentence, similar to the English gerund (-ing forms):

Spanish uses the infinitive after any preposition that requires a verb form. Once again, English uses the gerund form in these cases.

Whenever two verbs are used together in Spanish, the first must be conjugated while the second remains in infinitive form. One of the main groups of verbs that require the use of infinitives after them are modal verbs. However, some commonly-used transitive verbs also need infinitives after them. In this case, the infinitive is the complement of the verb. For example:

When the infinitive follows a conjugated verb, the object pronouns and reflexive pronouns can either come before the conjugated verb or attach to the infinitive. But if no conjugated form accompanies the infinitive, the pronoun has to attach to its ending and cannot come before the infinitive.