The expansive Kogod Courtyard will probably be popular for private events and fundraisers. (Roman_Lutsenko/Smithsonian American Art Museum)

If it’s been your lifelong dream to say “I do” to your Prince Charming in a real castle, the Smithsonian Institution has your fantasy covered.

In a major shift that will make some of Washington’s most impressive public spaces available for personal use, the federally funded Smithsonian has decided to rent its signature spaces for such celebrations as weddings, engagement and retirement parties, and proms and other teen events.

As of March 1, individuals, nonprofit groups and corporations can host parties in more than a dozen venues, including the Renwick Gallery’s elegant Grand Ballroom, the entire National Zoo, the Natural History Museum’s iconic rotunda and the spacious Kogod Courtyard (shared by the Smithsonian American Art Museum and the National Portrait Gallery). Rental fees range from $1,000 for a conference room to $150,000 for the whole zoo. (Security, maintenance and other fees are extra.)

“There has long been high demand and high interest in using our beautiful spaces for life moments,” said Stephanie Stebich, director of the Smithsonian American Art Museum. “Imagine a longtime docent has a major birthday or anniversary. They want to come to the museum, they want to host their friends here, they want to say, ‘This is a special place for me.’ ”

The three-year pilot program will bring in much-needed revenue for the museums that make up the world’s largest cultural organization, which must raise about $500 million in earned revenue and donations each year to supplement its $1 billion annual federal subsidy. It will attract new visitors, too, and deepen relationships with the Smithsonian’s core audience, officials say.

“We have people who deeply love our museum, and whenever possible we want them to have an art moment,” Stebich said. “People create memories and associations with places that mark important moments in their lives. Let’s invite them in.”

The change allows the Smithsonian to catch up to other cultural organizations, including many in Washington. The National Building Museum, the National Archives and the National Museum of Women in the Arts are a few of spaces that already host such social events. The Kennedy Center, which opens its new space, the Reach, in September, plans to rent it out for private events.

It took more than two years for the policy to wend its way through the Smithsonian bureaucracy and receive approval. And the venues don’t come cheap. That fairy-tale wedding in the Castle on the Mall will cost about $15,000 for rental and security and maintenance fees. Rental fees for the Kogod Courtyard are $22,500 to $60,000, depending on the type and size of event. There’s an additional charge for keeping any gallery spaces open.

“We have these extraordinarily beautiful buildings, and the fact that we haven’t been able to make them available for nonprofit fundraisers and personal, joyful celebrations has felt like a wasted opportunity,” said Rachel Goslins, the director of the Smithsonian’s Arts and Industries Building.

The Smithsonian’s previous special-events policy, last updated in 2006, limited outside use of the federal buildings to co-sponsored events that individual museums would host for a donation. Yet despite the prohibition on private parties and outside fundraisers, many of the spaces were busy. The Smithsonian American Art Museum, for example, hosted 150 events last year, bringing in $1.1 million. In November and December alone, the museum held 15 parties, ranging from 800 people for an NPR reception to 200 for an anniversary party for the Hausfeld law firm.

The broader rules should increase special-events revenue by 20 percent, Stebich said.

“Currently I have three special-event staff,” she said. “I want to make sure I have the staff support. We have to deliver in terms of making it a memorable experience.”

Stebich and other Smithsonian officials are adamant that the private events won’t encroach on public programs. That could limit some of their appeal, since most museums are open to the public daily until 5:30 p.m.

Museum and research center directors decided which of five categories of special events they would host in their spaces and what types of events they would permit. If a museum accepted a category — such as corporate and nonprofit receptions or personal social events for adults — it will have to accept any group covered by it, said Karen Keller, director of Smithsonian special events and protocol. That means that an anti-climate-change group could hold a fundraiser in the Natural History Museum or that a white-nationalist group could seek space in the National Museum of African American History and Culture.

“We are federal buildings, so we cannot deny any group or organization based on viewpoint,” Keller said. The museums, however, can’t be rented for political events or public programs, such as a concert that would sell tickets to the public.

Event planners are enthusiastic about the availability of new venues.

“The city center has a limited number of venues for large groups,” said Aimee Griffin, owner of A. Griffin Events. “The idea of having beautiful architecture, a space that is interesting? We are excited.”

The Arts and Industries Building, the historic brick building next to the Smithsonian administration building on the southern edge of the Mall, is expected to be a popular choice because of its flexibility. The National Historic Landmark has no collection of artifacts or regular visitor hours, and its interiors can be sectioned off for small events or opened to accommodate 900 people seated and 2,000 standing. In fact, an evening reception there for 600 people was booked for April on the first day of the new policy.

“I get to make this beautiful space available and make money doing it,” said Goslins, its director. “Hard to think of a downside.”