In "Harry Potter", what subject is taught by Professor McGonagall?

Professor Minerva McGonagall is deputy Headmistress, head of Gryffindor House, Transfiguration professor, and later Headmistress at Hogwarts. She is first introduced in the opening chapter of "Harry Potter and the Philosopher's Stone", when she meets Dumbledore at Number 4 Privet Drive, Little Whinging, Surrey (the home of Harry's aunt and uncle, Vernon and Petunia Dursley).

McGonagall is described as a tall, rather severe-looking woman, with black hair typically drawn into a tight bun. She wears emerald green robes, a pointed hat, and always has a very prim expression. She speaks with a slight Scottish accent. She is, according to Rowling, a sprightly 70-year-old. McGonagall wears square spectacles that match the markings around the eyes of her Animagus form of a British Shorthair silver tabby cat; she has the distinction of being the first Animagus introduced in the series and being one of the few registered Animagi of the century, though she is rarely seen using the ability.

Harry's immediate impression of her is of someone who is not to be crossed. She has a fondness for tartan, and her handkerchief, at least one hat, dressing gown, and dress robes are patterned with it. In the films, McGonagall often wears a Scottish brooch of a specific Scots style set with Cairngorm citrines and Scottish agate.