The building itself was built prior to 1714, most likely in 1704. Before it became a restaurant, Hopestill Capen's dress goods business occupied the property. In 1771 printer Isaiah Thomas published his newspaper, The Massachusetts Spy, from the second floor. The restaurant originally opened as the Atwood & Bacon Oyster House on August 3, 1826.
The Union Oyster House has a number of famous people in history as diners, including the Kennedy clan and Daniel Webster. Webster was known for regularly consuming at least six plates of oysters. Perhaps most surprising, in 1796 Louis Philippe, king of France from 1830 to 1848, lived in exile on the second floor. He earned his living by teaching French to young women. Labor economist and president of Haverford College John Royston Coleman worked here incognito as a "salad-and-sandwich man" for a time in the 1970s and documented the experience in his book The Blue Collar Journal.
The food is traditional New England fare, including seafoods such as oysters, clams, and lobsters, as well as poultry, baked beans, steak and chops. The toothpick was said to have been popularized in America starting at the Oyster House.
According to wikipedia