There are excellent restaurants throughout Boston, and almost any cuisine - and fusion of cuisines you can think of will be served somewhere. The most popular restaurants do tend to be located around the busiest areas such as Back Bay, where you can find the elegant Restaurant Clio, and the gastronomic paradise of L'Espalier. (Both require reservations).
On Beacon Hill, the relaxed Persian restaurant Lala Rokh is a big draw, and South End is home to literally dozens of the more fashionable haunts.