That's only a part of the globalization of local church life. International visitors speak at churches all the time, email campaigns urge action to distribute malaria nets or assure decent wages for coffee pickers, bake sales raise funds for Haiti. Habitat for Humanity speaks of the "theology of the hammer," where groups working together live the spirit of "doing unto others."

These mission trips arouse a wide range of feelings; they extend from passionate support and admiration to cynicism and near contempt. That's a recipe for blithe, often incorrect assumptions.

Robert Wuthnow, a wise and prolific scholar of religion at Princeton University (where I served as a trustee) sets out to shed light on the phenomenon. His book Boundless Faith: the Global Outreach of American Churches is a fascinating exploration, based on a tough-minded survey and extensive interviews, of what America's Christian churches are doing in the international arena.

The first myth he seeks to dispel is that the 300,000-350,000 local congregations in the United States are turning inwards. Not so. A majority have some form of international ties. Wuthnow estimates they spend about $4 billion overseas a year. The numbers of Americans who work in what can roughly be called missions are also impressive. Some 43,000 Protestant church fulltime missionaries work overseas. Some 350,000 Americans spend from two weeks to up to a year abroad as short-term mission volunteers, and up to one million undertake a mission of less than two weeks.

These rough statistics give a glimpse of the complex ways in which congregations, by their very nature local, are being transformed, with the international links so broad and diverse that they defy the efforts of researchers to define and label.

There are competing and conflicting presumptions about what this mission work means, and what impact it has. Is it of a piece with America's noble destiny to improve the world, or is it more tied to a syndrome of the "ugly American," driven largely by a self image that is blind to the visions and strengths of people from other cultures and religions?

Wuthnow answers those questions with descriptions of the rich, dynamic, and complex kaleidoscope of congregations at work. Individually the projects and impact may be small and there are hazards in trying to add them up into a coherent whole. But religious congregations are increasingly players in larger economic and political dynamics, including international development. What may be most important is their role in linking the daily realities of communities to the larger realities of the interconnections in today's world. Local churches are vital to helping people understand why what happens in Malawi or Timor Leste matters for their children, and also helping them to find ways to translate that awareness into practice. Service helps but it can also transform the servers and their communities.

Wuthnow's book (recommended reading) probes deep into the complexities of the global dimension of American churches. There have always been tensions between Christian calls to serve others selflessly and to spread "the good news", but tensions are amplified by our increasing knowledge of other cultures and faiths and cultures. We can only hope that any lingering certainties about the rightness of "our way" are melting but debates about the ethics of proselytizing and hiring practices continue.

The mission work of churches is essentially about a call to America's conscience. Wuthnow is most persuasive as he underlines how important churches are in this collective challenge. Their mosaic "consists of preaching and teaching about Americans' common bond with and responsibility to be engaged with the rest of the world. It also includes thousands upon thousands of hours devoted to learning about the needs of people in other countries, hosting speakers, raising money, and organizing ways of getting people involved." Surely that's a contribution we should heed and support.

----Katherine Marshall is a senior fellow at Georgetown's Berkley Center for Religion, Peace and World Affairs, a Visiting Professor, and Executive Director of the World Faiths Development Dialogue.