The A-Team

The "A-Team" is a secret group of people who use the pseudonym "A" to threaten Alison DiLaurentis, Aria Montgomery, Hanna Marin, Spencer Hastings, and  Emily Fields. Mona is a member of the "A-Team," as revealed in "UnmAsked;" Toby Cavanaugh is a member of the "A-Team," as revealed in "The Lady Killer," Spencer Hastings is a member of the "A-Team," as revealed in "I'm Your Puppet" and "A dAngerous gAme." As revealed in the episode "The First Secret ", The A Team was created in October of 2008.

When Mona 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, Spencer asks her what she's going to do now, because doesn't "A" always have a plan? Mona replies with "Yes, she does." 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.

When Toby Cavanaugh was revealed to be the next "A," there were plans alluded that referred to a mysterious phone call, that never got made. Also it was mentioned that if he and Mona knew that Nate was going to Garrett Reynolds "off the hook" for Maya's murder then they would have done things differently. Toby's motives for being involved in the "A-Team" were to "keep Spencer safe" as revealed in A DAngerous GAme. This could also be the reason "A" saved Spencer from Ian in Season 1.

Season 1
Throughout season 1, the possibility of a team of A's tormenting the liars was practically unheard of. Both the fans and the liars were of the belief that A is only one person. This was mostly due to the fact that in the books, A (book character) is only one person, and a team of people has yet to be mentioned up to the present book.

However, despite its team status, the A, or rather the person in the black hoodie, who was after the liars was primarly one person (Mona Vanderwaal). After UnmAsked, Marlene King confirmed that Mona was the A who did everything to the liars in the first two seasons (except two things), despite the fact that Mona's actions were actually planned out and ordered by the Main A. Either way, however, there were always other people involved with Mona, even in the first two seasons.

Season 2
In season 2, the possibility of an A-Team was also ignored up until Touched by an 'A'-ngel. In the last few minutes of the episode, Spencer, Emily, Hanna and Aria talk about the possibility of A working with multiple people. At the time, the liars were suspecting Jenna and Garrett of being A, and that Jason killed Alison. The liars talked about how Jenna, Garrett and Jason were all working together, and "playing for the same team". This was the very first reference to the A-Team.

Later, in A Hot Piece of A, the liars begin to think that the person in the greenhouse wasn't actually A, but A's helper.

Throughout the season, the liars continue to suspect Jenna and Garret, and later, Melissa, of being A. They often refered to A as "them". By the end of the season 2 finale, most fans had an idea of there being more then one person. However, the current stucture of the A-Team was not thought of at the time. It was believed by many people that there is only one A, the person in the black hoodie, and that this "A" had helpers in case of emergency. It was not thought of there being multiple minor A's who wear a black hoodie, all controlled by a leader, the Big A, who wears a red coat. In "UnmAsked," Mona attends the Rosewood Masquerade Ball with the other girls and later goes with Spencer to the Lost Woods Resort, 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. She tells Mona that she changed her mind and that she'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 with a flashlight.

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 even though she survived

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 member of the A-team. While Mona is still in Radley Sanitarium, the Liars are still getting texts from "A". Also it is revealed that after the events of "Photoshop," Spencer, Aria and Hanna returned to "A"s lair and all of "A"s pictures of the liars had been removed. Spencer also mentions several occasions where Mona was with them at the same time they received texts from "A" proving that she has "friends" who help her.

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?"

In The Remains Of "A", Aria found a sack of money hidden in Ezra's sock drawer, which might mean that he was the one Jason Dilaurentis wrote a check to. This could possibly mean he is a member of the "A" team.

In "Single Fright Female", two black hoodied figures are seen together. One hands the other the room key to "Room A".

In "The Lady Killer", Nate St. Germain/Lyndon is revealed to have been Maya's killer. Mona walks with a black-hooded member of the A-Team back to Radley Sanitarium. Mona talks about how she wishes they could have made "the phone call", but says that even the best laid plans can go awry. She says to the A Team member, "I'll see her soon I guess." When they turn around, you see that the member is Toby.

During "This Is A Dark Ride", a little girl appears at Ashley's house. She is very cold and quiet. She is the little girl from the story Alison told in "The First Secret." She said, "My sister and I fight over everything. Even our dolls." In the story, the other little girl killed her sister because she took her doll after they fought over it. This could imply that Ali is A because that story had some characteristics of when Ali killed her twin sister in the book Courtney or Ali could still be alive harrassing Aria, Hannah, Emily and Spencer.

In "She's Better Now", Toby tries to run down Lucas. He's wearing his hoodie so possibly A is afraid that Lucas may reveal something he shouldn't. Later a hooded figure tampers with someone's bike and the person (Brad from Decathlon Club - in which Mona later takes his place) crashes

In "Misery Loves Company", Mona tells Toby she is not the one "calling the shots" and "they [the liars] need to understand that she's in charge", confirming A is indeed a girl.

In "Dead to Me", A member of the "A" team was seen, by a drugged Emily, digging Alison's grave. Big "A" was also there - to supervise - and leaves when Emily begins to yell stop. Spencer also found the second "A" lair, but it was empty.

In "I'm Your Puppet", Aria goes to pick up Malcolm from karate, but finds that he has already been picked up by an "Aria Montgomery". She goes to his cubbie and finds a carnival flyer with an A circled. Aria heads over to the carnival; while talking to her mom, she sees Malcolm getting a ballon with a black hoodie standing by him. Malcolm watches a puppet show and eats popcorn with a black gloved person. When she found him and hesaid Aria's "friend's" name is "Alison". Spencer is shown putting her pills in her pillow and takes out a black hoodie, along with two puppet show tickets, and thinks about how she joined the "A" team, meaning it was her who took Malcolm.

In "A Dangerous GAme", the other Liars learn that Spencer is on the A-Team and unbeknownst to Mona; Toby and Spencer infiltrated for the same reason: Spencer wanted to protect the other girls and Toby while he confirmed that did it to protect her

Members
Confirmed:

Alison Dilaurentis (revealed to be Red Coat, though it is still unknown if she is Big A; since she was seen in a hallucinating environment)

Mona Vanderwaal (after "UnmAsked " threatened to stay, and after A dAngerous gAme, expelled off the team)

Toby Cavanaugh (joined to protect Spencer, not an actual member)

Spencer Hastings (joined to find information; not an actual member)

Unknown girl who Toby saw

Unknow person who hit Toby

Unconfirmed:

Shana

Jenna Marshall

Melissa Hastings

A's Lair
A's lair is "A|A's" base of operations. It is where "A" would meet up with the other A's, and plan. The original lair was 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. Spencer concludes that A was stalking Alison. This is where Spencer figures out Mona is "A," due to the gum wrapper and cashmere sweaters.

Once the original lair was discovered by Spencer, the other A's cleared out the room and began to find and rent a new room elsewhere for the lair. We know the new lair is "Room A" of its building, and is basically an exact replica of the original lair. Mona was seen in the lair in "The Lady Killer" discussing plans with another 'A', presumably Toby. In "Dead to Me", Spencer finds the second lair, with the help of a PI, but it is empty when she arrives.

The lair is currently being housed in an R.V.; which explains there ability to be anywhere they need.

Trivia

 * In the season 2 finale, UnmAsked Mona was revealed to be A, and we see a person in a red coat visiting her at the end in Radely. Mona looks up, and says: "I did everything you've asked me to do!" This tells us that Mona is in fact a minor "A" working for the Big "A". One could argue that although Toby and Mona are both "A", they are simply the minor "A"'s, but not the Main "A", or as some fans like to call it, the Big "A".
 * Toby has been revealed to be the second A- team member.
 * Some fans suspect Aria of being A because she was the last person to have Vivian Darkbloom's (the alter ego of Alison DiLaurentis) red trench coat, which the leader of the A- team/Big A has been known to wear.
 * A popular theory of the members of the A team is: A (Alison), T (Toby), E (Ezra), A (Aria) and M (Mona)= -A TEAM.
 * 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 Melissa, 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."
 * The leader of the team could be the mystery person seen at the end of UnmAsked wearing a red coat, just as it could be the same person seen at the end of "Blood Is The New Black", while wearing a red hoodie buying black hoodies and gloves from a man, who asks whether "A" is buying this merchandise for a "team."
 * 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. This is most likely Emily's massage (She was with Hanna) and killing Ian (She has no known connection to him, and he clearly knew the person that pushed him off the bell-tower.)
 * It's possible the leader is a woman. In "UnmAsked,"  Spencer asked if "A" always has a plan. Mona answered, "Yes, she does."
 * In "The Kahn Game" we see "A" coming to Mrs. Pillsbury (who is obsessed with cats) to rent a room/apartment. Mrs. Pillsbury names "A" as 'dear' and talks to her which makes it obvious that this "A" is female.
 * It's possible that the leader wears red while the recruiters wear black. Such as the person who visited Mona at Radley.
 * We have seen "A", or someone persumed to be A, in many diffrent disguises: the red coat (the main A) person, the baby face Halloween costume and the Queen of Hearts costume. This leads us to question the size of the A-Team.
 * Hanna finds the key to "Room A" in 316 misery loves company.
 * Ashley Benson said that there are a few members of the A-Team and we will know who they are during the season.
 * "A" carries around Vivian Darkbloom's driver license and uses it
 * In the Season 3 Finale, Spencer follows a figure in a red coat into the Girls Bathroom at Rosewood High, thinking it's the leader. She turns her round, but it is Hanna dressed in the coat, part of a plan formed by the Liars (sans Spencer).
 * After the fire at the Thornhill lodge, Hanna, Emily and Aria are pulled out by somebody. Hanna looks up to see Alison staring back at her, in a Red Coat. This confirms that Alison DiLaurentis is Red Coat, and effectively, Big A.

Season 1

 * Jenna Marshall - She meets an unseen person in the park and hands them an unknown item with the instructions "You know what to do." She was also seen associating with the Black Swan. Jenna hates the Liars for being involved in The Jenna Thing. Moved Det. Wilden's body with Shana after Ashley ran him over. (Seasons 1, 2, 3, 4)
 * Ian Thomas - May have started the N.A.T. Club to film people for someone other than himself, Jason, and Garrett.
 * Toby Cavanaugh - Ali forced him to lie about The Jenna Thing. (Season 1, 3)
 * Noel Kahn - He has dated both Mona and Jenna, and hates Aria for cheating on him with Ezra. (Seasons 1, 2, 3)
 * Alison DiLaurentis-Lots of people think that Alison or  possibly her twin is on the A team. (Season 1, 2, 3, 4)

Season 2

 * Jason DiLaurentis. He almost hit Ali with a hockey stick. There were also pictures of Aria in his shed. In "She's Better Now" He and Mona are hanging out and he has a screwdiver sized hole in his side, and he disappeared when the liars appeared in the hospital. (Season 2, 3)
 * Garrett Reynolds - He gave a page from Ali's autopsy report to Jenna to hold onto. (Season 2, 3)
 * Melissa Hastings - She hated Ali for dating Ian at the same time as her, so she threatened her. She is also the Black Swan. (Seasons 2, 3)

Season 3

 * Paige McCullers - She has a violent past with Alison and also in A's contacts in her phone
 * Lucas Gottesman - He had molyzapam pills in his camera bag. Also, Alison used to bully him and the girls made no attempts to stop her. (Seasons 2, 3)
 * Ezra Fitz - Suspiciously hid cash after we saw Jason writing a check. Also seems to be having mood swings recently as well as in the Halloween special of Season 3 acted suspicious when Aria saw him on the train.
 * CeCe Drake - Was believed to to be Red Coat and was with Alison in Cape May during Labor Day Weekend.
 * Shana - Met Jenna in secret to spy on the Liars. Moved Det. Wilden's body with Jenna after Ashley ran him over. (Season 3, 4)
 * Duncan Albert - Big A/Alison came to the Hastings' cabin with an airplane, similar to the one Duncan has. He probably is some sort of "assistant".