Subjective precognition

Clairvoyance is the ability to gain information using mechanisms other than the five senses. Alice Cullen of the Olympic Coven is the only one shown to have this ability. It's known that Aro is dying to have this kind of ability.

Description
Alice can get visions of the future, sometimes at will. At first she couldn't control them, but she gained it during her growth as a vampire. She can use it to keep tab of things by merely focusing on the subject. She has also described that some visions come to her when there is a connection between her and the source of the vision; whether it be a threat to her family or simply someone she relates to.

Limitations
Her visions are subjective; she can only see the future once a decision affecting it has been made, and some visions are more certain than others.

She can see vampires and, less clearly, humans. She cannot see werewolves/shapeshifters or hybrids, because, as she says, "she had never been one". The closer, or 'attuned', she is to a person, the clearer she can see him or her.

In Eclipse, Alice explains that since her visions are no illusion of the mind, but rooted into reality, they can affect Bella. This is at a variance with the gifts, such as Jane's capability to inflict the illusion of pain, of other vampires that are connected to the mind.

Below are some of the visions that Alice experiences in the Twilight Saga.

Pre-Twilight
Before Twilight, because of her visions, still human Alice was interned in an asylum. She was saved by an unknown compassionate vampire, who changed her to protect her from the tracker James. Alice smelt beyond mouth-watering to James; so she was changed so that James could not kill her. Though her creator was destroyed, Alice determinedly searched for the one person in most of her visions -- Jasper. After the two finally met, they searched for the Cullens with help from Alice's visions because they wanted to have a family and to help Jasper become 'more vegetarian'. They haven't left the family since.

Twilight
In Twilight, Alice sees Bella becoming a vampire, and that it would storm at the baseball clearing. She also sees Laurent, Victoria and James coming towards the clearing after they hear the game, but since it was a snap decision, there was no way to run or to hide Bella. After they run to Phoenix, Alice sees James meeting Bella at the ballet studio and at Bella's house. It can also be assumed that she also sees Bella running from Jasper, but that it was too late to stop her. When they get to the ballet studio, they save her even though she is severely injured. When recreating a scene for Bella's accident, Edward says "Alice had a little too much fun gathering evidence".

New Moon
In New Moon, Alice saw Bella jumping off a cliff, and assumed she had committed suicide because she couldn't see Jacob, him being a shapeshifter (though she didn't know it at the time). Alice becomes very unconfortable when she can't see something because of a shapeshifter. She told Rosalie while she went to Forks to see Charlie, There, Bella who explained what she was doing and about the Quileute tribe. Later, Edward, posing as Carlisle, calls Charlie to check on Rosalie telling the truth about Bella being dead. Jacob answered and told Edward that Charlie was at a funeral. Alice revealed that Edward thought the funeral was Bella's, and that she really was dead. They rushed to Volterra, Italy, to prevent Edward from committing suicide as well, and Alice saw visions of him trying to think up ways to get himself killed, but his changing his mind so quickly made almost impossible for her to tell final decision. Bella managed to stop him in time, but they were all, including Alice, brought to the Volturi, who asked them to join. They declined. When Caius demanded Bella dead because of her knowledge of vampires, Alice shows Aro a vision of Bella becoming a vampire. They were then set free, and Alice later voted that Bella become a vampire.

Eclipse
In Eclipse, Alice sees a vision of Victoria being back in town. After Edward leaves Bella in her care, she sees Bella running off to La Push with Jacob, but cannot stop her. Afterwards, during the mysterious string of Seattle murders, the family realizes a vampire is behind it that knows of Alice's gift as they are changing their minds so fast. When they realize it's an army of newborn vampires, they start training and try to enlist the help of the Denali Coven. However they refuse since Irina is still upset over Laurent's death at the hands of the wolves. So, the wolf pack wind up helping, even though Alice cannot see them. Eventually, they realize Victoria is behind the army along with her new partner Riley and the Cullens wait up in the snowy woods to wait out the fight. Thanks to Alice's gift, the fight is successful and the Cullens win after Edward destroys Victoria, and Seth Clearwater destroys Riley. Before the arrival of the Volturi, it is revealed that Alice is irritated with Jasper as he wouldn't let her fight and, as a result, she bites him.

Breaking Dawn
During Breaking Dawn, Alice cannot see Bella because of her pregnancy with Renesmee, and most of the coven initially believes it's a boy. She explains to Jacob that it gives her a headache to try and see, and since she cannot see at all with him around, her headache gets lessened. After Renesmee is born, and Irina reports her to the Volturi, Alice and Jasper leave, instructing the family to gather as many witnesses as they can. Alice sends various others along on her travels, and eventually reappears at the final confrontation with several other vampires, and the hybrid, Nahuel. Nahuel informs the gathering that he, his sisters and Renesmee are not of any danger of exposure, and the Volturi leave in peace. When everyone confronts Alice about her disappearance, she apologizes and admits she took so long, because she was trying to look for what she couldn't see in her visions, like it was a blind spot.

Midnight Sun
In Midnight Sun, Alice's visions are more clearly as Edward sees them along with her. It is revealed that she saw him leaving, Tyler's car crash, Bella becoming her best friend, Edward supposedly killing Bella, Jasper's attempts to kill Bella, Edward blocking him, and, finally, Edward falling in love with Bella.