Muggle-borns inherit magic from a distant ancestor; they are descended from Squibs who have married Muggles and whose families had lost the knowledge of their wizarding legacy. The magic resurfaces unexpectedly many generations later.

Because of the heritable traits of magic, Muggle-born siblings are possible, as in the case of Colin and Dennis Creevey. However, this is not always the case, as Lily Evans' sister Petunia was a Muggle.

When Muggle-born witches and wizards reach the age of eleven in the British wizarding community, their Hogwarts acceptance letters are delivered in person by a member of the staff, instead of by owl post (the usual postal system for wizards and witches). The purpose is to reassure the parents or guardians about the sudden news, and explain to them about the concealed magical society. They would also assist the family with the preparation for going to their desired wizarding school and for the buying of school supplies.