Anti-Judaism denotes a spectrum of historical and contemporary ideologies that are fundamentally or partially rooted in opposition to Judaism. It encompasses the rejection or abrogation of the Mosaic covenant and advocates for the supersession of Judaism and Jewish identity by proponents of other religious, political-ideological, or theological frameworks, which assert their own precedence as the "light unto the nations" or as the chosen people of God. The opposition is often perpetuated through the reinterpretation and appropriation of Jewish prophecy and texts, reflecting a complex interplay of belief systems that challenge Jews' internally and externally conceived distinctiveness. David Nirenberg posits that the theme has manifested throughout history, including in contemporary and early Christianity, Islam, nationalism, Enlightenment rationalism, and in socioeconomic contexts.

Douglas R. A. Hare found at least three anti-Judaisms in history. The first is prophetic anti-Judaism: the criticism of Judaism's beliefs and religious practices. The second is Jewish Christian anti-Judaism: the form taken amongst Jews who believe that Jesus of Nazareth was the Jewish Messiah. The third type he defined was gentilizing anti-Judaism, which emphasizes the gentile character of the new movement (i.e., Christianity) and asserts God's formal rejection of Jews as a people. Most scholarly analyses appear concerned with the phenomenon described by his third type.

According to Gavin I. Langmuir, anti-Judaism is based on "total or partial opposition to Judaism as a religion—and the total or partial opposition to Jews as adherents of it—by persons who accept a competing system of beliefs and practices and consider certain genuine Judaic beliefs and practices inferior."

As the rejection of a particular religion or particular way of thinking about God, anti-Judaism is distinct from antisemitism. An example of religious anti-Judaism is the Islamic doctrine known as tahrif.

The term "anti-Jewish" is often colloquially used interchangeably with terms such as "anti-Semitic", "anti-Hebrew", or "anti-Judaism". Although these designations share a commonality – hatred towards a group of people – each term encompasses unique ideologies and prejudices. Jeanne Favret-Saada, author of "A Fuzzy Distinction: Anti-Judaism and Anti-Semitism" explains the ways in which historians often conflate anti-Judaism and anti-Semitism, failing to distinguish between Christian anti-Judaism and Nazi anti-Semitism. Favret-Saada argues that the combination of these distinct ideologies diminishes the Christian role in the evolution from anti-Judaism to anti-Semitism. Anti-Judaism encapsulates those who oppose the Jewish religion and religious system. The term refers to Christian animosity towards Judaism as a religion. Anti-Judaism historically included attempts to convert Jews to Christianity. In contrast, the term "anti-Semitic" is more modern and secular term, categorizing Jews as a racial or ethnic group. Anti-semites hate and target Jews for their biological Jewish identity rather than religious beliefs.

In Ancient Rome, religion was an integral part of the civil government. Beginning with the Roman Senate's declaration of the divinity of Julius Caesar on 1 January 42 BC, some Emperors were proclaimed gods on Earth, and demanded to be worshiped accordingly throughout the Roman Empire. This created religious difficulties for those Jews, monotheistic, who adhere strictly to their customary law, and worshipers of Mithras, Sabazius and early Christians. At the time of Jesus' ministry, the Jews of the Roman Empire were a respected and privileged minority whose influence was enhanced by a relatively high level of literacy. The Jews were granted a number of concessions by the Romans (the right to observe the Sabbath and to substitute prayers for the emperor in place of participation in the imperial cult). They had been exempted from military service on the Sabbath, for example. Julius Caesar, who never forgot the debt he owed to Antipater the Idumaean for playing a decisive role in the Battle of Pelusium and thereby saving his life and career, was supportive of Jews, allowing them uniquely a right to assembly and to collect funds for Jerusalem. His enmity toward Pompey, who had conquered Jerusalem and defiled the Holy of Holies, enhanced his status among them, as he ordered the reconstruction of the walls of Jerusalem after the destruction wrought by Pompey. He may also have cultivated Jews as clients to buttress his position in the East against the latter. At times he treated the high priest Hyrcanus II on equal terms by writing to him as Rome's pontifex maximus. Jews reacted to his assassination by mourning him publicly in Rome.

The crisis under Caligula (37–41) has been proposed as the "first open break between Rome and the Jews", even though problems were already evident during the Census of Quirinius in 6 and under Sejanus (before 31).

After the Jewish-Roman wars (66–135), Hadrian changed the name of Iudaea province to Syria Palaestina and Jerusalem to Aelia Capitolina in an attempt to erase the historical ties of the Jewish people to the region. Although this idea has been pointed out as a mere assumption, with no basis in historical sources, according to other scholars. After 70, Jews and Jewish proselytes were only allowed to practice their religion if they paid the Jewish tax, and after 135 were barred from Jerusalem except for the day of Tisha B'Av. Frequent Jewish uprisings (two major wars in 66–73 and 133–136 CE, in addition to uprisings in Alexandria and Cyrene), xenophobia, and Jewish prerogatives and idiosyncrasies, were at the root of anti-Jewish feelings in some segments of Roman society. These confrontations did cause temporary erosions in the status of the Jews in the empire. Reversals in the relationship were temporary and did not have permanent or sustained impact.