Atossa (Old Persian: Utauθa, or Old Iranian: Hutauθa; 550–475 BC) was an Achaemenid empress. She was the daughter of Cyrus the Great, the sister of Cambyses II, the wife of Darius the Great, the mother of Xerxes the Great and the grandmother of Artaxerxes I.

The Persian name "Atossa" (or "Atusa") means "bestowing very richly" or "well trickling" or "well granting". Atossa is the Greek (Ancient Greek: Ἄτοσσα) transliteration of the Old Persian name Utauθa. Her name in Avestan is Hutaosā.

Queen Atossa is the most famous bearer of this name, however, the name Atossa appears to have been a traditional one within the Achaemenid clan. According to the genealogy of the Kings of Cappadocia, the name Atossa was also borne by a sister of Cambyses I and sister-wife of Artaxerxes II.

Atossa was born in 550 BCE as the eldest daughter of Cyrus the Great and his wife Cassandane. Cassandane, an Achaemenian and the daughter of Pharnaspes, bore Cyrus two sons, Cambyses II and Bardiya, as well as three daughters: Atossa, Artystone, and Roxane. Cyrus and Cassandane were known to share a deeply loving relationship. Following the death of Cyrus, both Atossa and Artystone were married to Darius the Great.

Atossa was first married to her brother, Cambyses II, the son and successor of Cyrus the Great, as his first consort. In Achaemenid Persia, marriages between close family members, such as half-siblings, nieces, and cousins, were not uncommon and were not regarded as incestuous, yet brother-sister and father-daughter marriages were frowned upon. According to Herodotus, Cambyses supposedly married two of his sisters, Atossa and Roxane. This would have been regarded as illegal. However, Herodotus also states that Cambyses married Otanes' daughter Phaidyme, whilst his contemporary Ctesias names Roxane as Cambyses' wife, but she is not referred to as his sister. Hence it remains problematic to determine the reliability of these accounts.

Accusations against Cambyses for committing incest are used as a way to vilify him: painting him as mad and vain. This is a common historiographical issue faced in many older historical texts on Persia. For example, one of the primary records of his incestuous acts is from an Egyptian text which antagonizes many of his actions, far beyond incest. However, many of the allegations within the text, such as the killing of the Apis bull, have been confirmed as false, which means that the report of Cambyses' supposed incestuous acts are also contestable.

Atossa bore no children with Cambyses, and his reign concluded abruptly with his death in the spring or summer of 522 BCE.

Following Cambyses’ death, the empire entered a period of political instability. A usurper named Gaumata , who claimed to be Bardiya (Cambyses’ younger brother and the son of Cyrus the Great), seized power. Bardiya’s death was not known to the public, which allowed Gaumata, a Magian priest from Media, to proclaim himself king near the Persian town of Paishiyauvada. During this tumultuous period, Atossa was passed into Gaumata’s harem. This situation was short-lived however, as Darius the Great overthrew Gaumata, took possession of the harem and claimed the throne. To legitimize his rule, Darius took wives from the noblest houses of Persia, marrying Cyrus' daughters Atossa and Artystone, as well as Parmys, Atossa’s niece. Atossa was granted the status of Darius’ primary consort and queen.