Hellenistic Judaism was a form of Judaism in classical antiquity that combined Jewish religious tradition with elements of Hellenistic culture and religion. Until the early Muslim conquests of the eastern Mediterranean, the main centers of Hellenistic Judaism were Alexandria in Egypt and Antioch in Syria (modern-day Turkey), the two main Greek urban settlements of the Middle East and North Africa, both founded in the end of the 4th century BCE in the wake of the conquests of Alexander the Great. Hellenistic Judaism also existed in Jerusalem during the Second Temple Period, where there was a conflict between Hellenizers and traditionalists.

The major literary product of the contact between Second Temple Judaism and Hellenistic culture is the Septuagint translation of the Hebrew Bible from Biblical Hebrew and Biblical Aramaic to Koine Greek, specifically, Jewish Koine Greek. Mentionable are also the philosophic and ethical treatises of Philo and the historiographical works of the other Hellenistic Jewish authors.

The decline of Hellenistic Judaism began in the 2nd century, and the precise causes are not fully understood. Following the Roman suppression of the Diaspora Revolt (115–117 CE), Jewish populations in Egypt, including the large and influential community in Alexandria, as well as those in Cyrenaica and Cyprus, were eradicated. Jewish presence in these regions was not re-established until centuries later, without regaining their former influence. Over time, much of the Greek-speaking diaspora was incorporated into the rabbinic framework by the rabbis. Additionally, it is possible that some members of Hellenistic Jewry were marginalized, absorbed, or gradually became part of the Koine-speaking core of early Christianity centered on Antioch and its traditions, such as the Melkite Greek Catholic Church and the Greek Orthodox Patriarchate of Antioch.

The conquests of Alexander the Great in the late 4th century BCE spread Greek culture and colonization—a process of cultural change called Hellenization—over non-Greek lands including the Levant. This gave rise to the Hellenistic period, which sought to create a common or universal culture in the Alexandrian empire based on that of fifth-century Athens, along with a fusion of Near Eastern cultures. The period is characterized by a new wave of Greek colonization which established Greek cities and kingdoms in Asia and Africa, the most famous being Alexandria in Egypt. New cities established composed of colonists from different parts of the Greek world and not from a specific metropolis ("mother city") as before.

The spread of Hellenism caused a blending of the local indigenous culture and the culture of the conquerors. Jewish life in both Judea and the diaspora was influenced by the culture and language of Hellenism. Local indigenous elites frequently played a significant role in embracing and promoting Hellenism, leading to its impact on all regional cultures, including the Jewish culture. In Judea, Hellenism gradually took hold, despite the relatively small number of foreign inhabitants.

The Jews living in countries west of the Levant formed the Hellenistic diaspora. The Egyptian diaspora is the most well known of these. Indeed, there was firm economic integration of Judea with the Ptolemaic Kingdom that ruled from Alexandria, while there were friendly relations between the royal court and the leaders of the Jewish community. This was a diaspora of choice, not of imposition. Information is less robust regarding diasporas in other territories. It suggests that the situation was by and large the same as it was in Egypt.

The Greeks viewed Jewish culture favorably, while Hellenism gained adherents among the Jews. While Hellenism has sometimes been presented (under the influence of 2 Maccabees, notably a work in Koine Greek) as a threat of assimilation diametrically opposed to Jewish tradition,

Adaptation to Hellenic culture did not require compromise of Jewish precepts or conscience. When a Greek gymnasium was introduced into Jerusalem, it was installed by a Jewish High Priest. And other priests soon engaged in wrestling matches in the palaestra. They plainly did not reckon such activities as undermining their priestly duties.