Sheba, or Saba, was an ancient South Arabian kingdom that existed in Yemen before 275 BCE. It likely began to exist between c. 1000 BCE and c. 800 BCE. Its inhabitants were the Sabaeans, who, as a people, were indissociable from the kingdom itself for much of the 1st millennium BCE. Modern historians agree that the heartland of the Sabaean civilization was located in the region around Marib and Sirwah. In some periods, they expanded to much of modern Yemen and even parts of the Horn of Africa, particularly Eritrea and Ethiopia. The kingdom's native language was Sabaic, which was a variety of Old South Arabian.

Among South Arabians and Abyssinians, Sheba's name carried prestige, as it was widely considered to be the birthplace of South Arabian civilization as a whole. The first Sabaean kingdom lasted from the 8th century BCE to the 1st century BCE: this kingdom can be divided into the "mukarrib" period, where it reigned supreme over all of South Arabia; and the "kingly" period, a long period of decline to the neighbouring kingdoms of Ma'in, Hadhramaut, and Qataban, ultimately ending when a newer neighbour, Himyar, annexed them. Sheba was originally confined to the region of Marib (its capital city) and its surroundings. At its height, it encompassed much of the southwestern parts of the Arabian Peninsula before eventually declining to the regions of Marib. However, it re-emerged from the 1st to 3rd centuries CE. During this time, a secondary capital was founded at Sanaa, which is also the capital city of modern Yemen. Around 275 CE, the Sabaean civilization came to a permanent end in the aftermath of another Himyarite annexation.

The Sabaeans, like the other South Arabian kingdoms of their time, took part in the extremely lucrative spice trade, especially including frankincense and myrrh. They left behind many inscriptions in the monumental Ancient South Arabian script, as well as numerous documents in the related cursive Zabūr script. Their interaction with African societies in the Horn is attested by numerous traces, including inscriptions and temples dating back to the Sabaean presence in Africa.

The Hebrew Bible references the kingdom in an account describing the interactions between King Solomon of Israel and a figure identified as the Queen of Sheba. The Hebrew Bible's account is considered legendary. A similar narrative is also found in the Quran (Sheba is distinct from the Sabians). Traditions concerning the legacy of the Queen of Sheba feature extensively in Ethiopian Christianity, particularly Orthodox Tewahedo, and among Yemenis today. She is left unnamed in Jewish tradition, but is known as Makeda in Ethiopian tradition and as Bilqis in Arab and Islamic tradition. According to the Jewish historian Josephus, Sheba was the home of Princess Tharbis, a Cushite who is said to have been the wife of Moses before he married Zipporah. Some Quranic exegetes identified Sheba with the People of Tubba.

The Sabaic language was written down in the Sabaic script as early as the 11th or 10th centuries BCE. The Sabaic tradition has left behind a sizable epigraphic record. Of the 12,000 corresponding Ancient South Arabian inscriptions, 6,500 are in Sabaic. The region first sees a continuous record of epigraphic documentation in the 8th century BCE, which lasts until the 9th century CE, long after the fall of the Sabaean kingdom and covering a time range of about a millennium and a half and constituting the main source of information about the Sabaeans. South Arabian civilization may be the only civilization that can be reconstructed from epigraphic evidence.

External information about the Sabaeans comes first from Akkadian cuneiform texts starting in the 8th century BCE. Less important are brief reports from the Bible about correspondence between Solomon and the Queen of Sheba. The story is considered legendary as early first-millennium BC epigraphic sources show no evidence of diplomatic missions or women rulers. Knowledge of the Sabaeans as merchant peoples indicates that some level of trade between the regions was underway in this time. After the campaigns of Alexander the Great, South Arabia became a hub of trade routes linking the broader geopolitical realm with India. As such, information about the region begins to appear among Greco-Roman observers and information becomes more concrete. The most important accounts about South Arabia are from Eratosthenes, Strabo, Theophrastus, Pliny the Elder, an anonymous first-century seafarming manual called the Periplus of the Erythraean Sea concerning the politics and topography of South Arabian coasts, the Ecclesiastical History by Philostorgius, and Procopius.

Scholars have noted that Sheba and ancient Judah/Palestine maintained trade, linguistic, and cultural contacts during antiquity.

The formative phase of the Sabaeans, or the period prior to the emergence of urban cultures in South Arabia, can be placed the latter part of the 2nd millennium BCE, and was completed by the 10th century BCE, where a fully developed script appears in combination with the technological prowess to construct complex architectural complexes and cities. There is some debate as to the degree to which the movement out of the formative phase was channeled by endogenous processes, or the transfer or technologies from other centers, perhaps via trade and immigration.