The arts are all about diversity, of course, but in the theatre world, it can be difficult to draw certain lines. Can a black actor play Hamlet? If so, can a white actor play Othello, whose race is central to the play that bears his name? And what about accents? Must actors performing Shakespeare all use a standard, stock ‘Shakespeare’ accent? (Think Laurence Olivier or John Gielgud.)Increasingly, the answer has been that ‘mixed casting’ is not only allowable, but useful in many situations, and even the most staid and conservative companies are starting to experiment. Case in point: the venerable Royal Shakespeare Company, which has been raising some eyebrows during a residency in Washington, D.C.