A pro-drop language (from "pronoun-dropping") is a language where certain classes of pronouns may be omitted when they can be pragmatically or grammatically inferable. The precise conditions vary from language to language, and can be quite intricate. The phenomenon of "pronoun-dropping" is part of the larger topic of zero or null anaphora. The connection between pro-drop languages, and null anaphora relates to the fact that a dropped pronoun has referential properties, and so is crucially not a null dummy pronoun.

Pro-drop is licensed only in languages that have a positive setting of the pro-drop parameter, which allows the null element to be identified by its governor.

Pro-drop is a problem when translating to a non-pro-drop language such as English, which requires the pronoun to be added, especially noticeable in machine translation. Amongst other reasons, it can also pose a problem with respect to transfer errors and second language acquisition.

An areal feature of many northern European languages is that pronoun dropping is not, or seldom, possible (see Standard Average European); this is the case for English, French, German, and Emilian, among others. In contrast, Japanese, Mandarin Chinese, Slavic languages, Finno-Ugric languages, and Hebrew exhibit frequent pro-drop features. Some languages, such as Hindi, Greek, and European Portuguese, have the ability to pro-drop any argument.