What are the role of fairies in Shakespeare's A Midsummer Night's Dream?

The most obvious role of the fairies in A Midsummer Night's Dream is simply that they contribute to the magical, otherworldly atmosphere of the play. The fairies and their behavior are also described in very much human terms, and the significance of this is to convey the impression that the human world and the world of fairies are not as separate as one might think.
However, there are three fairy characters who are especially significant in the play for different reasons. Oberon, the fairy king, is significant because his role, in part, is to bring the lovers together. The second especially significant fairy character is Oberon's wife, Titania. Oberon and Titania's relationship plays a significant role in the play because it points to the theme of power. The power struggle between them affects the seasons and the crops. This suggests that the desire for power can be destructive.
The third especially significant fairy character is, of course, Puck. Puck is significant because he is responsible for much of the comedy in the play. He turns Bottom's head into the head of a donkey, for example. He transforms himself into a stool and then disappears when old women try to sit down on him. He is also responsible for much of the confusion in the play, and confusion is a key element of comedy. Puck's role, therefore, is very much to be the main comic force in the play.