AQ, Aq, aQ, or aq may stand for or refer to:

• Aq, alternate name of Ak, Buin Zahra, a village in Iran
• American Samoa, the DAFIF 0413 / DIA 65-18 / FIPS PUB 10-4
• Antarctica, ISO 3166-1 country code
• L'Aquila, a province of Italy

.aq is the Internet country code top-level domain (ccTLD) for Antarctica. It is reserved for organizations that conduct work in Antarctica or promote the Antarctic and Southern Ocean regions. It is administered by Peter Mott of Mott and Associates of Auckland, New Zealand.

An aqueous solution is a solution in which the solvent is water. It is usually shown in chemical equations by appending (aq) to the relevant chemical formula. For example, a solution of table salt, or sodium chloride (NaCl), in water would be represented as NaCl(aq). The word aqueous means pertaining to, related to, similar to, or dissolved in water. As water is an excellent solvent and is also naturally abundant, it is a ubiquitous solvent in chemistry.