The owners of the Natick Mall in Boston are the latest to jump on the mixed-use center bandwagon. They're planning a $150 million, 550,000-square-foot expansion that would include 65 new stores, four restaurants, and 250 luxury condominiums in two eight-story towers. “This is the wave of the future that has finally reached Massachusetts,” says William Wheaton, research director at the Center for Real Estate at the Massachusetts Institute of Technology. “Developers nationwide are building housing around shopping centers because people want to be within walking distance of movies, shops, and restaurants.” Typically located in a city's downtown area, mixed-use centers are a melting pot of retail stores, restaurants, theaters, sports arenas, cultural centers, residential units, and office spaces. Some are enclosed in two towers like the Natick Mall expansion or the AOL Time Warner Center in New York City, but the more common setup is in a village-like, open-air public space that invites social interaction like City Place in West Palm Beach, Fla. It's designed to look like a European town center complete with sidewalk cafes, fountains, salons, shops, a comedy club, and a '20s church that's been transformed into a cultural center. Mixed-use centers are becoming increasingly popular across the country and even worldwide, and developers are looking at them as a way to revitalize a city and encourage a sense of community.