The A-Team

The "A-Team" may be a secret group of people who use the psuedonym "A" to threaten the liars Aria Montgomery, Hanna Marin, Spencer Hastings, Emily Fields, and Alison DiLaurentis while she was still alive. Mona is the only known member of the "A-Team" thus far, as revealed in "UnmAsked."

When Mona Vanderwall was revealed to be "A," she tried to convince Spencer Hastings to join, what she referred to as, the "A-Team." She also alludes to it when she says "You had to earn it, the right to be a part of it." After Mona was admitted into the Radley Sanitarium, we hear in her mind that everything is going exactly as they planned. A mysterious person in a red jacket visited her and Mona told her that she did everything she told her to do.

Season 1
In "Keep Your Friends Close," the summer season finale of season one, the climax is reached when Hanna seems to figure out who "A" is, while spying in the forest. But before she can reveal the identity of "A," she is run down by a car while running to the other liars, and loses consciousness. Just then, the girls receive a text from "A" claiming responsibility for the hit-and-run.

Later in the hospital, in "Moments Later," Hanna tells the girls that Noel Kahn wrote the message on the back of Ezra's car, and he is presumed to be "A." (However, this is proved untrue when "A" plants the answers to three midterms in Noel Kahn's locker, because he was going to tell the principal that Aria and Ezra were dating.) "A" also leaves a message for Hanna on her cast, meaning that they had paid Hanna a secret visit in her hospital room.

In "For Whom the Bell Tolls," "A" saves Spencer from being murdered by Ian. "A" kills Ian in the process by hanging him. "A" takes Ian's body with him/her.

Season 2
In UnmAsked, Mona attends the Rosewood Masquerade Ball with the other girls and later goes with Spencer to the Lost Woods hotel, after Spencer deduces that A had rented the room next to the one Alison was staying in. In the room, they find sketches of a Black Swan costume and conclude that A must be wearing it at the ball. Mona offers Spencer a stick of gum, but Spencer turns her down. While going through A's belongings, Spencer locates a gum wrapper from the same brand of gum Mona just offered her. He tells Mona that he changed his mind and that he'd like a stick of gum after all. Mona agrees, but says she doesn't have any more on her, but that she can go get some out of her car while she goes to call Hanna. She leaves the hotel room while Spencer continues to search. A few minutes later, Mona returns to the room and angrily says "I found the gum!" Spencer looks up from the book and says "You didn't call Hanna...because you're A." Spencer turns around and we see Mona wearing a black hoodie. Mona admits she's A and congratulates Spencer on figuring it out, right before knocking her out.

Spencer wakes up in a car with Mona driving recklessly towards Lookout Point. Mona says that she wants Spencer to join the A-team. Spencer asks if the reason Mona became A was her anger at them for letting Alison bully her. Mona laughs and says that she got over that a long time ago. Mona reveals that she became A because she hated them for stealing Hanna's friendship from her. Spencer pleads with Mona to stop, encouraging her that Hanna is still her friend. As they drive, Spencer is secretly recording their conversation on her phone and sending the video to Aria's phone. Aria, Hanna, and Emily leave the ball immediately and drive to Lookout Point. When they show up, Spencer and Mona struggle, resulting in Mona falling off the edge. Spencer reaches out, trying to save her, but fails.

Mona was later put in Radley Sanitarium where she is visited by a mysterious stranger in a red jacket who seems to be the one giving "A" orders.

Season 3
In Season 3 it is confirmed that Mona isn't the only "A." While Mona is still in Radley Sanitarium, the Liars are still getting texts from "A". Also it is revealed that after the events of "UnmAsked," Spencer, Aria and Hanna returned to A's lair and all of A's posessions had been removed. Spencer also mentions several occasions where Mona was with them at the same time they recieved texts from "A," proving that Mona wasn't the one who sent those messages. This implies that at least one other "A" exists.

At the end of Blood Is The New Black, the new "A" is seen buying various black sweaters and gloves while wearing a red hoodie. The cashier says, "You buying this for a team?"

Mona Vanderwall
To date the only known identity of "A" is Mona Vanderwall. She is possibly working for an anonymous character that wears a long red trench coat. However, it is revealed at the end of the episode that Mona could simply be a worker for the stranger in the coat. It seems impossible that Mona is the only "A" because she is seen getting a text from "A" while in Hanna's room, though nothing is absolutely clear. Mona is good at hacking so it is possible that she could of programmed the phone to send the text. Or she could be aided by someone, possibly the red coated stranger. Because of the alliance it is still uncertain if Mona is the original "A" or if "A" recruited her later in the series to pose as "A" in some instances. (ex. Threatening Anne Sullivan, following Spencer to the motel). This would make sense since Mona's motive was that the girls were stealing Hanna away from her, and the girls started getting text from "A" before the 4 girls got close again.

A's Lair
A's lair is "A's" base of operations. It is where "A" would go to think of plans, send texts, create messages, and find ways to torture the girls. Its is located in Room 2 of the Lost Woods Resort. The room contains pictures, newspaper clippings, and dolls resembling the girls and Alison. There is a hole in the wall behind a picture frame so "A" could watch Alison in Room 1 next door. This is where Spencer figures out Mona is "A," due to the gum wrapper and cashmere sweaters. It is also where Mona reveals herself to be "A" and knocks Spencer out.

Trivia

 * In "UnmAsked," Jenna, Lucas and the Black Swan are seen together. Considering the events of the Season 2 season finale, the Black Swan may be a member, which suggests that Jenna and Lucas are also part of the "A-Team."
 * It's further speculated that Jenna Marshall is on the A-team because during "UnmAsked," she meets an unseen person in the park and hands them an unknown item with the instructions "you know what to do." Some believe this person to be the same person who visits Mona at the end. This might make sense if Mona and Jenna formed a friendship after Halloween 2008, as alluded to in "The First Secret." This would might also mean Noel is on the A-Team, since he had been helping Jenna and the whole relationship and breakup with Mona was staged.
 * In "Blind Dates," "A" sends Emily a box of Danby merchandise and handwritten note which reads "SO HAPPY TO HAVE YOU ON OUR A -TEAM!"
 * Producers revealed Mona didn't do two of the things "A" did.
 * The next of the "A-Team" members will be revealed in The Remains Of The "A"