100 Light Street (colloquially known by its most recent former label, the Transamerica Tower) is a 40-story, 528 ft (161 m) skyscraper completed in 1973 in downtown Baltimore, Maryland.

Later occupied by and known as the Legg-Mason Building, the structure faces the former "The Basin" of the Helen Delich Bentley Port of Baltimore on the Northwest Branch of the Patapsco River and the Inner Harbor downtown business waterfront redevelopment.

The tower was one of the first skyscrapers to be constructed using a then-revolutionary method of erecting a towering central reinforced concrete column first containing elevators and service infrastructure conduits and then followed later by the surrounding scaffolding or steel horizontal beams rising floor by floor, and was a magnet for "sidewalk superintendents" and passing office workers during its construction during the early 70's.

Overlooking the new harborfront parkland and expanded bulkheads of former Sam Smith Park with newly rebuilt/repaved Light and Pratt Streets with median strips and landscaped tree-lined sidewalks focused on a brick waterside promenade, soon to be anchored by the historic sailing U.S. Navy warship, USS Constellation (originally thought to be from 1797, later documented as 1854) with "Constellation Dock" replacing old Municipal Pier 1.

Construction of the new rising tower challenged for the first time forty years the "tallest tower" ranking held since its 1929 completion of the art deco-styled former Baltimore Trust Company Building, (which later went bankrupt shortly after its completion after the Great Wall Street Stock Market Crash of October 1929), then assumed several other names before bearing the title of the Maryland National Bank of the reorganized old B.T.C., by the 1960s soon the largest banking chain in the state.

It was also the former home of Legg Mason investment and financial advisors who later relocated to newer quarters on the eastern side of the downtown in Harbor East.