Hellenistic Judaism was a form of Judaism in the ancient world that combined Jewish religious tradition with elements of Greek culture. Until the fall of the Roman Empire and the Muslim conquests of the Eastern Mediterranean, the main centers of Hellenistic Judaism were Alexandria (Egypt) and Antioch (Northern Syria—now Turkey), the two main Greek urban settlements of the Middle East and North Africa area, both founded at 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 conflict between Hellenizers and traditionalists (sometimes called Judaizers).

The major literary product of the contact of Second Temple Judaism and Hellenistic culture is the Septuagint translation of the Hebrew Bible from Biblical Hebrew and Biblical Aramaic to Koiné Greek, specifically, Jewish Koiné Greek.

The decline of Hellenistic Judaism started in the 2nd century CE, and its causes are still not fully understood. It may be that it was eventually marginalized by, partially absorbed into or became progressively the Koiné-speaking core of Early Christianity centered on Antioch and its traditions.