Ten years after the Guggenheim opened its extremely successful Frank Gehry outpost in Bilbao, a museum-building boom is occurring worldwide. From Los Angeles to Minneapolis to Abu Dhabi, new buildings designed by architects such as Renzo Piano, Herzog & de Meuron, and, of course, Mr. Gehry, are sprouting up everywhere.

In America, two dozen art museums have opened major expansions in the last decade, and a dozen more are currently engaged in building projects. In New York, these include the Museum of Modern Art, whose $425 million Yoshio Taniguchi building opened in 2004; the Morgan Library & Museum, which opened a $106 million expansion designed by Mr. Piano last year; the New Museum of Contemporary Art, which opens its new home on the Bowery next month, and the Whitney Museum of American Art, which is planning its own Renzo Piano branch in the meatpacking district.

Abroad, China is also going through a burst of building, with the construction of new museums such as the Shanghai Museum of Contemporary Art, funded by a Hong Kong jeweler; the Zendai Museum of Modern Art, funded by a real-estate development company; the state-owned Duolun Museum of Modern Art, and the Ullens Center for Contemporary Art, founded by a Belgian couple and opening this month in Beijing.

Meanwhile, the government of Abu Dhabi has announced its intention to build a $27 billion “cultural district” on Saadiyat Island. As planned, the district will include four museums — one of them a Gehry-designed Guggenheim, another a Louvre Abu Dhabi designed by Jean Nouvel — and a performing arts center designed by Zaha Hadid.

In 25 years, will this construction binge seem brilliant or foolish? Will it have advanced the mission of art museums, or merely diffused it? The answer may be very different in different places and for different projects.

In America, the push toward expansion has been driven by the sustained economic growth of the last decade, museums’ increasing focus on reaching diverse audiences, the obsolescence of facilities built in the mid-20th century, and the role of architecture as an expression of civic pride.

The Art Institute of Chicago’s new $283 million Modern Wing, designed by Mr. Piano and set to open in 2009, will add 65,000 square feet of gallery space and create a technologically up-todate, 20,000-square-foot education center.

It will also enhance the museum’s connection with a revitalized city center, the Art Institute’s director, James Cuno, said in an interview. The Modern Wing adjoins Millennium Park, an urban development project that includes a Frank Gehry-designed concert pavilion, ice rinks, an interactive fountain, and a monumental outdoor sculpture by Anish Kapoor. An elevated footbridge between the museum and the park will offer a view over the park and downtown.

“There’s a civic dimension to it,” Mr. Cuno said of the expansion, “a sense that the vitality of the museum reflects the vitality of the city.”

In some projects, however, the desire to distinguish a city through its museum architecture, à la Bilbao, has led to overreaching and financial strain.

The Denver Art Museum predicted that its new Daniel Libeskind building, which opened last fall, would draw a million visitors in its first year. In 2004, the museum’s director, Lewis Sharp, was quoted in the Rocky Mountain Newsassaying:”Ifyoulookatwhat the Guggenheim did for Bilbao, I believe this will do for Denver.” Well, it didn’t: Not only was the new building plagued by a leaky roof, but in its first year it received only 630,000 visitors, far short of expectations. Last spring, the museum was forced to cut staff in order to reduce the budget.

While the Milwaukee Art Museum was building its Santiago Calatrava addition, which opened in 2001, the Milwaukee Journal Sentinel quoted the museum’s executive director, Christopher Goldsmith, saying the museum’s goal was to “beat Bilbao!”

After the expansion opened, the museum did see a surge in attendance: around 500,000 visitors in the first year, and an average of 300,000 annually since then, which is almost double the 160,000 annually the museum received in the two years prior to the expansion.

At the same time, however, the cost of the expansion had ballooned to $100 million from $35 million. The museum went $25 million into debt and, despite the increased attendance, began running deficits. In 2002, a new director, David Gordon, was brought in; the debt is now paid off and the budget is balanced.

In an interview with The New York Sun, Mr. Gordon denied the museum was hoping to achieve a so-called “Bilbao effect.” He said the goal of the expansion was not necessarily to attract tourists, but “to put the museum on the map and put Milwaukee on the map, [so that] wherever you go internationally, people say, ‘Oh, Milwaukee, they have that amazing Calatrava building.'”

As many have pointed out, the success of the Guggenheim Bilbao is difficult, if not impossible, to replicate. The Basque government made an initial investment in the museum of more than $100 million and continues to provide ongoing support for operations and acquisitions. The museum was not a one-off project, but part of a regional economic development plan that also included a bridge and an airport terminal by Mr. Calatrava, a railway station designed by Norman Foster, a riverfront renewal project by Cesar Pelli, and several other commissions from celebrity architects.

In addition, the Guggenheim Bilbao benefited by being the first extraordinary-looking museum building. As Mr. Gordon noted: “Being second or third is not as much of a coup.”

Some museum leaders have criticized the priorities expressed in recent expansions. In an article in the journal Curator, the director of the Indianapolis Museum of Art, Maxwell Anderson, noted the emphasis on “soaring atriums, the potential for event income, shops, restaurants, and special exhibition galleries that host commercially-oriented blockbusters.” Instead of trying to turn themselves into theme parks, he argued, museums should focus their limited resources on collecting and conserving art.

Others say that expanding is often a prerequisite for attracting donations of art. “People are not going to give their art if they think it’s going to sit in storage,” the president of the American Association of Museums, Ford Bell, said in an interview with the Sun. As chairman of the Minneapolis Institute of Arts, Mr. Bell raised $103 million to build a new wing designed by Michael Graves.

In other parts of the world, major museum construction is driven not so much by hunger after a “Bilbao effect” as by the global movement of wealth, and the desire of newly rich countries to have cultural assets, such as museums and concert halls, to go with their Mercedes-Benz showrooms and Louis Vuitton stores. Individual works of art can be bought up at auction by newly minted billionaires, but institutions take longer to establish — hence the decision by the sheiks in Abu Dhabi to rent the names, collections, and expertise of Western museums.

For the “Old World” of Western Europe and America, the question is how to take advantage of these opportunities. “The world is tipping: You have cash-rich, assetpoor countries, and us, who are cash-poor and asset-rich,” the former art consultant, and now executive director of Jazz at Lincoln Center, Adrian Ellis, said. “We will become sources of programming.” In America, the only institution besides the Guggenheim to consider a foothold in Abu Dhabi is Lincoln Center for the Performing Arts, which is in talks — it’s not clear how serious — about providing programming for the performing arts center.

France, on the other hand, has fully embraced the idea of exporting its cultural heritage. In an interview with the Sun last March, France’s then minister of culture, Renaud Donnedieu de Vabres, called the Louvre deal “the beginning of a new French strategy of spreading our culture to the rest of the world.”

The strategy includes making high culture accessible to underservedpopulationswithinFrance, aswell. The$1.3billiontheFrench government received from Abu Dhabi in the Louvre deal should help pay for two other museum projects, both set to open in 2009: a new branch of the Pompidou Center in Metz, an industrial city in eastern France, and a Louvre outpost in Lens, a former mining city in the north.

Meanwhile, the Pompidou is also considering expanding to Shanghai.