Telepathy is the ability to hear human thoughts and read human minds. If Telepaths focus hard enough, they can "enter" another person's mind and penetrate their memories.
The ability to hear other people's thoughts makes it difficult for Sookie Stackhouse to talk to people, as she hears all their secrets and desires. This can cause problems, as most people think things they do not say because they think they are too spiteful or cruel. However, there are good points to being able to hear people's thoughts, as pointed out by Adele Stackhouse. She suggested that her husband Earl could also hear thoughts and, by using his ability, he stopped his brother Francis from killing himself.
If someone cannot control their ability properly, they will find it difficult to live in normal human society. Telepaths in the series can hear the thoughts of other supernatural creatures except vampires.
Telepaths are able to hear thoughts in the person's own voice; for example, when Rene had his mind read by Sookie, she noticed that he did not think with a Cajun accent, but rather with his real southern accent. ("You'll Be the Death of Me")
Sookie tried to release Tara Thornton from Maryann Forrester's mental hold, but was unable to read her. With Bill Compton's ability to glamour Tara into opening her mind, they were able to use their powers together and lift Maryann's spell.
While in Faery, Sookie uses her telepathy to speak to her grandfather, Earl. While speaking to him, warning him they need to leave, the other Faeries are able to hear her thoughts. ("She's Not There")
In Sookie's house, Bill requests Sookie try to read the mind of Doug, a local man who was glamoured by a powerful vampire. While Doug says he doesn't remember much, Sookie sees his memories of a woman approaching him, but is unable to see who it is. She then sees another memory of Doug's, this one involving the woman unearthing Russell Edgington, a powerful vampire who had been buried beneath the building Doug worked in. A terribly weak and blood deprived Russell is seen being held and Sookie notices the woman wearing the same pendant as those worn by members of the Authority.
In contrast to the television series, the book series states specifically that the gift of telepathy is rare, even in the supernatural community.
It is stated a few times that Sookie's power is not a gift common amongst the Fae. The TV series decided to ignore this in favor of solving the mystery early and made it a Fae trait.
It was revealed in the eleventh book Dead Reckoning that Sookie's powers come from Demons, specifically the demon Desmond Cataliades. He gave Sookies grandmother Adele a thimble of his blood in her wine so that any of her descendants who had the "essential spark" would be blessed with the power of telepathy (the "essential spark" being an openness to the other world, the world of the supernatural, and those born with it are destined for great things).