Jonathan Sarna is the Joseph H. and Belle R. Braun Professor of American Jewish History at Brandeis University. His new book, "American Judaism," is out this month from Yale University Press.

The title of your book is "American Judaism," rather than "American Jews." Can you explain the difference?
There have been quite a few histories of American Jews-that is, the Jewish people in America. But strangely we have not had, in half a century, a serious work on American Judaism, the religion of American Jews. How has it developed? How has it changed? What is its relationship to American religion? How has it been influenced by American Protestantism? Where does it stand today?

People who study American religion really have very little sense of how Judaism fits in to that story. How Jews have been affected by the great turning points-the various awakenings, the Civil War, the women's movement, and so forth. American Judaism is distinctive. It's very different than Judaism is in Israel or Europe.

What are the major differences between Judaism in Europe and here?
The first thing is there's no chief rabbi in America. There was an experiment with one [in the 1840s], but it didn't last. The failure is more significant than the fact that they tried it.

Most chief rabbis are recognized, in some respect, by the government. That's true in England, in France, and certainly in Israel. There's an individual who represents the Jewish religion to the government, someone who stands opposite the cardinal or the archbishop. Indeed, what we have in Judaism here, as we also have in Christianity, is a kind of free market. There's no central authority that says you can only be Jewish this way and not another way.

The whole structure of American Judaism, with different movements or denominations and no central authority, suggests that American Judaism is influenced by Protestantism. Anybody is free, without seeking permission from any chief rabbi or any government office, to open up their own synagogue and to worship God as a Jew in the way that they think best. It is very much a reflection of church-state separation and the way religion developed in the wake of the American Revolution.

This free-market approach to Judaism has often run counter to the idea of Jewish unity, both now and in the past.
Yes, no question about it. The issues we think of as contemporary actually have very deep roots in the American Jewish experience. Some of them are problems that we have been grappling with, literally, for 350 years.

The question is: What holds everybody together? At a certain point in my research I realized that just as what holds Protestants together is basically the fact that they are not Catholic, what holds Jews together is basically the fact that they are not Christian. That's what unites Jews. But on many other issues, they are greatly divided.

But it seems like this idea of Jewish unity is much more important to Jews than the idea of Protestant unity is to Protestants.
I think that's right. Jews still do think of themselves as kind of one large family, and like any family, they are perturbed when unity is lacking. Religions that are ethnically based are much more concerned about unity, about sharing certain common memories and values and goals than religions that are not ethnically based.

Can you offer a few of the examples of the way Protestant movements have affected Judaism?
I think the notion that there are many paths to God and many ways of being a Protestant deeply affected Jews. The idea that any community will have people of varying churches is so basic to the way Americans think. [The Reform movement in Judaism] certainly referred to Protestant teachings to justify the reforms they sought to institute.

Judaism, like Protestantism, has also experienced eras of revival. Lots of people wrongly imagine that Jews came to this country Orthodox, that each generation is a little less religious, and that eventually they intermarry and march down the aisle of a church. That's not the Judaism that I found. Rather, periods of decline, periods of revival-much like we see in the history of American religion as a whole. Indeed, eras such as the second Great Awakening [from the 1790s to the 1840s] saw a great deal of new interest in Judaism, a back-to-the-synagogue movement-new excitement, new experimentation.

In our own day, just as American Protestants and Catholics have grappled first with the issue of women, and more recently with the issue of gays, so we find American Judaism grappling with these issues. The issues of immigration are the issues that all of our movements and faiths confronted. How do you Americanize? What do you retain? What do you lose? To what extent should we live in an enclave, to what extent should we reach out to those of other faiths? These are debates that go on throughout American religion.