al- (Arabic: ٱلْـ, also romanized as el-, il-, and l- as pronounced in some varieties of Arabic), is the definite article in the Arabic language: a particle (ḥarf) whose function is to render the noun on which it is prefixed definite. For example, the word كتاب kitāb "book" can be made definite by prefixing it with al-, resulting in الكتاب al-kitāb "the book". Consequently, al- is typically translated as "the" in English.

Unlike most other Arabic particles, al- is always prefixed to another word and never stands alone. Consequently, many dictionaries do not list it, and it is almost invariably ignored in collation, as it is not an intrinsic part of the word.

Al- does not inflect for gender, number or grammatical case. The sound of the final -l consonant, however, can vary; when followed by a sun letter such as t, d, r, s, n and a few others, it assimilates to that sound, thus doubling it. For example: for "the Nile", one does not say al-Nīl, but an-Nīl. When followed by a moon letter, like m-, there is no assimilation: al-masjid ("the mosque"). This affects only the pronunciation and not the spelling of the article.