Thea von Harbou, Lang's wife, published a novel, Metropolis, which was published in an English translation in 1927. The film premiered in Germany in 1926, and a badly-edited version was released in America in 1927. Following the bankruptcy of the filmmakers, the American print seems to be be the only extant compy.
Several restored versions (all of them missing footage) were released in the 80s and 90s. [1]
The film was "rediscovered" in the 1980's, when American film director and producer Francis Ford Coppola brought out a restored version with a new soundtrack. [Can someone confirm this?]