The Sorting Ceremony

Originally the pointed wizard's hat of Godric Gryffindor, the Sorting Hat was bewitched by all four of the founders of Hogwarts with brains and some amount of personality. Its function is to determine which of the four Houses each new student will enter. It does so at the beginning of the start-of-term feast, when it is placed on a three-legged (sometimes four-legged) stool in front of the Great Hall. It then sings a long, rambling song of introduction, a different one each year but with the same basic information in it: how it was bewitched to perform the sorting and what the criteria are for the various houses. The first year students one by one place the Sorting Hat on their heads. Within a minute, it loudly proclaims the house for which they are best suited.