Several magical communication methods are available to the wizarding world.

Owls

By far the most popular method of communication is via owls. Owls are used for conveying packages, with multiple owls acting in concert to deliver heavier packages. Owls also deliver mail and newspapers, acting as a replacement for the postal service of the Muggle world. If an owl delivers something for which payment is expected, such as a newspaper, the recipient places the money in a small pouch attached to the owl's leg. Not only owls may be used; Sirius Black makes use of a tropical bird, likely a macaw, on one occasion. The Ministry of Magic regulates Owl Mail.

How the owls find the recipients of the letters they carry is not specifically stated. In some circumstances, letters have extremely explicit addresses on them (specifying rooms or locations inside of a building). Other times, there is no mention of an address, and the owl is simply told to whom to deliver. The Ministry of Magic used to use owls to deliver inter-office mail within the ministry building, but according to Mr. Weasley, the mess was incredible. Now the ministry uses enchanted memos, which fly throughout the building as paper aeroplanes, rather than owls.

In addition, though owls are portrayed as flying directly to the recipient of their package, it is implied that owl traffic can be monitored and even interrupted. There are several references to "the owls being watched" and Harry uses different owls to communicate with Sirius (his godfather) since his snowy owl, Hedwig, would supposedly attract too much attention. On one occasion Hedwig is injured after being intercepted and searched (supposedly by Umbridge).

Patronuses

A Patronus is primarily used to repel Dementors. They can also be used for communication by accomplished witches and wizards. Albus Dumbledore devised a method of using Patronuses to deliver vocal messages, putting this to the exclusive use of the Order of the Phoenix. Dumbledore, Minerva McGonagall, Kingsley Shacklebolt, and Arthur Weasley all deliver messages via Patronus in the course of the series. McGonagall is also the only character in the series to have shown the ability to project multiple Patronuses to send multiple messages. Patronuses are also the only known way of repelling Lethifolds.

Severus Snape used his Patronus to lead Harry Potter to the forest pool wherein Gryffindor's sword was hidden in The Deathly Hallows.

Floo Network

While the Floo Network (a play on the word 'flue') is intended for use as a method of transport, it also occasionally serves as a method of communication. A wizard can throw a pinch of Floo Powder into a lit fireplace connected to the Network and put his/her head into the flames, causing it to appear in the fireplace of the wizard with whom he/she intends to speak. This use of the Network is first seen in Harry Potter and the Goblet of Fire when Harry sees Amos Diggory's head in the Weasleys' fireplace at The Burrow, talking to Molly Weasley. Harry also uses this method to communicate with Sirius Black on several occasions during the series.

The etiquette surrounding using the fireplace for communication is not explicitly addressed in the series. Dumbledore tells Harry it is not polite for a wizard to apparate (appear out of thin air) directly into another wizard's house. However, at one point Harry uses Floo Powder to contact Grimmauld Place unannounced. Severus Snape uses a fireplace to contact Remus Lupin and tell him he wants a word, before speaking to him in person in Harry Potter and the Prisoner of Azkaban.

Dark magic communication

Lord Voldemort uses a method of communication called the Dark Mark, which is like a brand on the inner forearms of the Death Eaters. When the mark is pressed, contact is made with other Death Eaters and Voldemort himself. Pressing one's Dark Mark causes every other Death Eater's mark to burn, signalling them to Disapparate from wherever they were and immediately Apparate to Voldemort's side.

Those who follow Voldemort consider the Dark Mark to be of great importance, and while some people are 'lucky' enough to have one, the privilege is restricted to those of 'pure' blood. It is stated that Fenrir Greyback (a vicious werewolf) is not allowed the Dark Mark, which is likely because he is a werewolf.

Hermione uses the principle of the Dark Mark in Harry Potter and the Order of the Phoenix. Instead of burning/engraving the message into the members of Dumbledore's Army's skin, she uses fake Galleons which all mimic each other and have messages on the rim. Later Malfoy and Madam Rosmerta, who was under the Imperius Curse, used Galleons to contact each other.

Other forms of communication

Apart from the fake Galleons enchanted by Hermione for Dumbledore's Army, there are a few other methods of closed-channel communications used in the books and films. Subjects painted into wizarding portraits are frequently used to carry messages between locations where their portraits hang. Phineas Nigellus (former Hogwarts headmaster and member of the Black Family) is used to send messages between Dumbledore's office and his other portrait in Grimmauld Place. Hermione takes Phineas from Grimmauld Place during Harry Potter and the Deathly Hallows and uses Phineas to obtain information about events at Hogwarts. Dumbledore also uses two other former headmasters in a similar fashion when Arthur Weasley is attacked by Nagini in the Ministry of Magic. A portrait is also seen carrying messages between the Minister for Magic and the Muggle Prime Minister in the opening of Harry Potter and the Half-Blood Prince.

Another form of closed communication used in the books and films is a set of mirrors that belonged to Sirius Black. Sirius gives Harry one mirror in Harry Potter and the Order of the Phoenix, with a note explaining to Harry that Sirius and James Potter used to use the mirrors to talk to each other when they were put in separate detentions. In Harry Potter and the Deathly Hallows, Harry uses a shard of his broken mirror to call for help from the Malfoy's cellar, and later finds out that Aberforth Dumbledore had been watching over Harry using Sirius' mirror, which he obtained from Mundungus Fletcher.

Flying paper aeroplanes (referred to as "interdepartmental memos") are used within the Ministry of Magic. In Harry Potter and the Order of the Phoenix when Arthur Weasley takes Harry to the Ministry of Magic, Mr. Weasley explains that these took the place of the owls to minimise the mess. They are pale violet with MINISTRY OF MAGIC stamped along the edges of the wings. A variation on this method of communication is shown in the film version of Harry Potter and the Prizoner of Azkaban, when Draco Malfoy sends Harry a note in class in the form of a flying paper crane.