The term "Judeo-Christian" was invented during World War II, when Christians started realizing how rude it was to rail against the Nazis for violating "Christian decency" since so many of the Nazi victims were Jewish. It was a superficial attempt to appear diverse and inclusive. Usually when I see the term used, the author actually is only talking about Christianity, and thus denies the truly different nature of Judaism.

The term Judeo-Christian does not have a lengthy history.

"It was during the Hitler years that American philo-Semites invented the 'Judeo-Christian tradition' to combat innocent, or not so innocent, language that spoke of a totalitarian assault on 'Christian civilization.'"

Peter Novick, Holocaust in American Life

That sentence footnotes Mark Silk, "Notes on the Judeo-Christian Tradition in America," American Quarterly 36 (Spring 1984), pp.65-85, which I have read, but can't seem to find right now.

Here's what the Oxford English Dictionary says about the history of the term:

• The earliest use of the phrase "Judeo-Christian" came in 1899 Lit. Guide 1 Oct. 146/1: "The total abandonment of the Judaeo-Christian 'continuity' theory." This sentence implies that Judaism and Christianity are NOT equivalent though there may be some continuity from one to the other.
• The next use is in 1910, Encycl. Brit. VI. 494/1: "The Clementine literature throws light upon a very obscure phase of Christian development, that of Judaeo-Christianity." Again, it's "very obscure" and only refers to a brief "phase" of Christian development. It doesn't apply to contemporary practices or beliefs of the two faiths or imply broader grounds for comparison between the religions.
• Then comes WWII, with a 1939 reference in New English Weekly 27 July 237/2 to "The Judaeo-Christian scheme of morals" which fits in with Novick and Silk's comments that this was an attempt at universalizing "Christian" terms and shoehorning Jews in as a matter of inclusiveness.
• The earliest reference to a "Judaeo-Christian deity" wasn't until 1957, and it wasn't until 1960 that "Judeo-Christianity" appeared.

As Novick and Silk point out and the OED verifies, the phrase "Judeo-Christian" was initially adopted out of altruistic motivations -- trying to rally and unite the nation. "Christian society" accomodated Jews by inclusively saying "Judeo-Christian" instead.

Unfortunately, all too often, that word merely replaces the word "Christian" without any deeper look at the underlying concepts, thus evoking a popular image that Judaism and Christianity have more in common than they actually do. Usually, that errs by making Judaism seem more Christian than vice-versa.

I remember an amusing/annoying letter to the Boston Globe from someone that praised the Christian Coalition's devotion to "Judeo-Christian values" and listed the organizations that embody those values -- all 100% Christian groups, none REMOTELY Jewish.

It's like use of the universal male -- you have to be careful when it switches from general to specific or it falls apart.

"A doctor is a busy person; he must be able to balance a million obligations at once. Dr. Jones is no exception -- a clinic to run, medical students to supervise, and a husband with polio."

http://www.english.upenn.edu/~cjacobso/gender.html

There are some missionary and proselytizing groups who purposely blur the distinction between the faiths to lure the less educated away from Judaism. And because of this mistaken notion of "Judeo-Christianity," in the last year or so, I've often found myself having to correct other posters' misconceptions about Judaism, explaining over and over again that Jews do NOT follow various Christian beliefs and practices.

I think the term "Judeo-Christian" is overused and usually misused. It really should only apply in certain very limited circumstances, because the differences between the religions are so broad and fundamental that its rare to actually refer to both at the same time.

All I ask is for people to be careful when they're using the term to make sure they're referring to BOTH religions.

A few quotes for whoever is interested:

"It is a mistake to believe that Christianity is the decendent of modern Judaism. Instead, it is much closer to the truth to state that from the matrix of ideas surrounding the end of the Second Temple era emerged two religions, Christianity and rabbinical Judaism, both of which claimed continuity with the original religion. They are not parent and child; they are brothers. As were Cain and Abel."

John Dominic Crossan, The Birth of Christianity, 1999

"Judaism is Judaism because it rejects Christianity; and Christianity is Christianity because it rejects Judaism."

Rabbi Eliezar Berkowitz,
chairman Jewish philosophy department at Hebrew Theological College, 1966

I also found http://www.biblebelievers.org.au/judeochr.htm to be a very interesting article from the Christian POV.