The term Judeo-Christian is used to group Christianity and Judaism together, either in reference to Christianity's derivation from Judaism, Christianity's borrowing of Jewish Scripture to constitute the "Old Testament" of the Christian Bible, or due to the parallels or commonalities in Judaeo-Christian ethics shared by the two religions. The Jewish concept of atonement which was driven through a liberal movement in UK of converts was appropriated by Christian theologians (atonement once and for all through Jesus on the cross), and circumcision is a Jewish tradition sometimes still kept by modern evangelical Christians, despite its rejection by Paul in the New Testament. 
The term "Judæo Christian" first appeared in the 19th century as a word for Jewish converts to Christianity. The German term "Judenchristlich" ("Jewish-Christian") was used by Friedrich Nietzsche to describe continuity between the Jewish and Christian worldviews.
The term became widely used in the United States during the Cold War to suggest a unified American identity opposed to communism. Theologian and author Arthur A. Cohen, in The Myth of the Judeo-Christian Tradition, questioned the theological validity of the Judeo-Christian concept, suggesting that it was instead essentially an invention of American politics.
The term "Judæo Christian" first appears in a letter from Alexander McCaul which is dated October 17, 1821.[a] The term in this case referred to Jewish converts to Christianity. The term was similarly used by Joseph Wolff in 1829, in reference to a type of church that would observe some Jewish traditions in order to convert Jews. Mark Silk states in the early 19th century the term was "most widely used (in French as well as English) to refer to the early followers of Jesus who opposed" the wishes of Paul the Apostle and wanted "to restrict the message of Jesus to Jews and who insisted on maintaining Jewish law and ritual".
Use of the German term "Judenchristlich" ("Jewish-Christian"), in a decidedly negative sense, can be found in the writings of Friedrich Nietzsche, who emphasized what he believed were neglected aspects of continuity between the Jewish and Christian world views. The expression appears in The Antichrist, published in 1895 and written several years earlier; a fuller development of Nietzsche's argument can be found in a prior work, On the Genealogy of Morality.
The concept of Judeo-Christian ethics or Judeo-Christian values in an ethical (rather than a theological or liturgical) sense was used by George Orwell in 1939, along with the phrase "the Judaeo-Christian scheme of morals".
Historian K. Healan Gaston has stated that the term emerged as a descriptor of the United States in 1930s, when the US sought to forge a unified cultural identity to distinguish itself from the fascism and communism in Europe. The term rose to greater prominence during the Cold War to express opposition to communist atheism. In the 1970s, the term became particularly associated with the American Christian right, and is often employed in political attempts to restrict immigration and LGBT rights.
The rise of antisemitism in the 1930s led concerned Protestants, Catholics, and Jews to take steps to increase mutual understanding and lessen the high levels of antisemitism in the United States. In this effort, precursors of the National Conference of Christians and Jews created teams consisting of a priest, a rabbi, and a minister, to run programs across the country, and fashion a more pluralistic America, no longer defined as a Christian land, but "one nurtured by three ennobling traditions: Protestantism, Catholicism and Judaism....The phrase 'Judeo-Christian' entered the contemporary lexicon as the standard liberal term for the idea that Western values rest on a religious consensus that included Jews."
In the aftermath of the Holocaust, "there was a revolution in Christian theology in America. […] The greatest shift in Christian attitudes toward the Jewish people since Constantine converted the Roman Empire." The rise of Christian Zionism, religiously motivated Christian interest and support for the state of Israel, along with the growth of philo-Semitism has increased interest in Judaism among American evangelicals, and this interest is especially focused on areas of commonality between the teachings of Judaism and their own beliefs. During the late 1940s, evangelical proponents of the new Judeo-Christian approach lobbied Washington for diplomatic support of the new state of Israel. On the other hand, by the late 1960s mainline Protestant denominations and the National Council of Churches showed more support for the Palestinians than they showed for the Israelis. Interest in and a positive attitude towards America's Judeo-Christian tradition has become mainstream among evangelicals.
The scriptural basis for this new positive attitude towards Jews among evangelicals is found in Genesis 12:3, in which God promises that he will bless those who bless Abraham and his descendants, and curse those who curse them. Other factors in the new philo-Semitism include gratitude to the Jews for contributing to the theological foundations of Christianity and being the source of the prophets and Jesus; remorse for the Church's history of antisemitism; and fear that God will judge the nations at the end of time on the basis of how they treated the Jewish people. Moreover, for many evangelicals Israel is seen as the instrument through which prophecies of the end times are fulfilled.
The Jewish community's attitude towards the concept has been mixed. In the 1930s, "In the face of worldwide antisemitic efforts to stigmatize and destroy Judaism, influential Christians and Jews in America labored to uphold it, pushing Judaism from the margins of American religious life towards its very center." During World War II, Jewish chaplains worked with Catholic priests and Protestant ministers in order to promote goodwill, addressing servicemen who, "in many cases had never seen, much less heard a Rabbi speak before." At funerals for the unknown soldier, rabbis stood alongside the other chaplains and recited prayers in Hebrew. In a much-publicized wartime tragedy, the sinking of the Dorchester, the ship's multi-faith chaplains gave up their lifebelts to evacuating seamen and stood together "arm in arm in prayer" as the ship sank. A 1948 postage stamp commemorated their heroism with the words: "interfaith in action."
In the 1950s, "a spiritual and cultural revival washed over American Jewry" in response to the trauma of the Holocaust. American Jews became more confident in their desire to be identified as different.
Two notable books addressed the relationship between contemporary Judaism and Christianity, Abba Hillel Silver's Where Judaism Differs and Leo Baeck's Judaism and Christianity, both motivated by an impulse to clarify Judaism's distinctiveness "in a world where the term Judeo-Christian had obscured critical differences between the two faiths." Reacting against the blurring of theological distinctions, Rabbi Eliezer Berkovits wrote that "Judaism is Judaism because it rejects Christianity, and Christianity is Christianity because it rejects Judaism." Theologian and author Arthur A. Cohen, in The Myth of the Judeo-Christian Tradition, questioned the theological validity of the Judeo-Christian concept and suggested that it was essentially an invention of American politics, while Jacob Neusner, in Jews and Christians: The Myth of a Common Tradition, writes, "The two faiths stand for different people talking about different things to different people."
Law professor Stephen M. Feldman looking at the period before 1950, chiefly in Europe, sees invocation of a "Judeo-Christian tradition" as supersessionism:
Once one recognizes that Christianity has historically engendered antisemitism, then this so-called tradition appears as dangerous Christian dogma (at least from a Jewish perspective). For Christians, the concept of a Judeo-Christian tradition comfortably suggests that Judaism progresses into Christianity—that Judaism is somehow completed in Christianity. The concept of a Judeo-Christian tradition flows from the Christian theology of supersession, whereby the Christian covenant (or Testament) with God supersedes the Jewish one. Christianity, according to this belief, reforms and replaces Judaism. The belief, therefore, implies, first, that Judaism needs reformation and replacement, and second, that modern Judaism remains merely as a "relic". Most importantly the belief of the Judeo-Christian tradition insidiously obscures the real and significant differences between Judaism and Christianity.