Patronus Charm

The Patronus Charm is a very difficult spell featured in the Harry Potter series of fantasy novels by J. K. Rowling. It is the only known means of defence against Dementors.

The Patronus Charm creates a projection of the caster's most positive feelings, like happiness, hope and the desire to survive, in the form of a silvery, insubstantial, semi-transparent avatar called the Patronus. In essence, a Patronus is the exact opposite of a Dementor. Even though it embodies all the good emotions a Dementor feeds on, a Patronus cannot feel despair and thus Dementors cannot hurt it. In that way, the Patronus can shield its caster from Dementors and even drive them away.

The form a Patronus takes is unique and always the same for every person who casts it. Harry Potter's Patronus takes the form of a stag, into which his father could transform because he was an Animagus. Hermione Granger's Patronus is an otter, which according to J. K. Rowling is Hermione's favourite animal.

The Patronus Charm is simple to cast in theory, but hard in practice. All the wizard or witch needs to do is to utter the incantation Expecto patronum (meaning I call/summon the protector) while holding a magic wand. In order for the spell to work properly, however, the caster must focus all of his or her positive feelings into it. This is a very difficult thing to do, considering the spell is supposed to be used when one is surrounded by the happiness-sucking Dementors.

The process can be made easier if the caster concentrates on a single, very happy memory. Such memories for Harry Potter include the moment when he learnt he was a wizard and would go to Hogwarts, or Dolores Umbridge being fired from Headmistress of the school.

According to Fantastic Beasts and Where to Find Them, the Patronus Charm is also the only known spell that can deal with Lethifolds, horrible creatures that look like black shrouds and silently slip into houses to suffocate and digest their victims.