Mia comes back to town with her dance troupe and invites Charlie to her performance. At first, he decides not to go and tries to convince Alan that he no longer has feelings for her. He goes to the see the performance and Mia explains that she wants some of Charlie’s sperm. Charlie responds by asking Mia for something.

Charlie and Mia start making their wedding arrangements. Things begin to fall apart when their two families meet each other. They eventually decide on a small ceremony in Las Vegas.

Berta discovers that Alan has been dating her daughter Naomi.

Rose is moving to London, and Charlie is surprised by his reaction to the news. Alan lies to a woman he met online.

Charlie and Linda get closer to consummating their relationship, but Charlie has trouble focusing when he begins to see Rose's face everywhere he turns.

Charlie has to come up with ways to keep his girlfriend's 4-year-old amused; Alan becomes a test subject.

Charlie's girlfriend is embrassed to go out in public with him. Meanwhile, Jake sneaks out to attend a concert.

When Alan finds himself wanting to break up with a woman, Charlie offers his expertise.

Rose returns from England, and plays nurse rather oddly for an ill Charlie.

Alan finds out some surprising information about Judith's sex life when he decides to go on a date with one of her friends.

Charlie double-dates with Jake and fixes Alan up with a hooker.

Alan feels Charlie is unable to control his womanizing ways.

In the 6th season opener, Charlie runs into an ex-girlfriend and a child who bears a striking resemblance to Charlie.

Charlie borrowed money from Alan and on the day he is supposed to pay him back, Alan goes to ask Charlie for the money. He again finds Charlie in bed with a beautiful woman. After Charlie shoos him out and assures him he'll get the money for him later that day, the woman asks if Charlie is really out of cash and Charlie tells her not to worry, that he has plenty of hooker money.

Alan is sure that things will turn bad when Charlie starts dating his receptionist.

When Judith kicks Herb to the curb, Alan comes knocking; Jake is sent to stay with a less-than-willing Charlie for three months during Judith's meltdown.

Alan tries to escape Judith's grasp as Charlie and Herb go on the prowl to pick up women. They later end up going back to Herb's hotel room with two prostitutes, where Herb declares his love for Judith and races over to win her back.

Charlie's admission that he's in love with Chelsea gets a surprising reaction from her

Chelsea's illness gives Charlie a chance to prove he can take care of her, but also yearning to run away from the situation.

After Chelsea discovers a nude picture of another woman on Charlie's cell phone, he blows off steam by going out for a night of drinking with Alan, Herb and his neighbor.

Charlie's desperate to make sure Chelsea and Evelyn don't befriend each other following their first meeting.

Chelsea is asked by Alan to arrange a blind date between he and her new friend, unaware that her new friend is Rose.

Charlie must make a difficult decision about his future and with which woman he wants to spend his life: Chelsea or Mia.

When Chelsea convinces Charlie to let Alan's new girlfriend, Melissa, move in, the girls end up taking over Charlie's house.

Alan ends up playing maid to Judith's new baby as well as his former mother-in-law. Meanwhile, Jake uses an incriminating photo to blackmail Charlie.

Alan starts working for Evelyn as Charlie works to fix the relationship between Chelsea and Jake.

Jake stops at nothing to get away from Charlie and Alan, after they embarrass him out in public.

Alan's advice to Chelsea that she get breast-reduction surgery is not met with enthusiasm by Charlie, who kicks him out, but staying with Evelyn has its own challenges.

Alan and Charlie are shocked when they wake up next to a strange woman, and try to find out what happened.

While overcoming a bad break-up, Chelsea invites her beautiful college roommate to stay at the house.

While Alan struggles to cure his baldness, Charlie deals with the problem that he can't satisfy Chelsea.

Chelsea wants Charlie to take dancing lessons for the wedding, when Charlie uncovers the truth that Chelsea has been lying about her finances.

Jake is taught the art of infidelity by Charlie, while Celeste is away for Christmas.

Jake hopes to win back Celeste by writing her love songs. Alan and Herb hope to keep Judith from finding out they've become friends.

Charlie opts to have a colonoscopy in order to avoid going on a trip with Chelsea to see her parents. However, when he returns home, he finds her parents at his house.

Charlie suspects Chelsea likes the lawyer representing Alan after his arrest for a bar fight.

Chelsea and Charlie's relationship is at risk when Charlie's jealousy comes between them.

Charlie runs off to Vegas and returns with a new wife, but she's not Chelsea.

Charlie and Chelsea have a post-breakup one-night stand.

Charlie has a return engagement with Chelsea's best friend, while Alan has an unexpected effect on a new female patient.

Alan is torn between the bad influence of Jake's new friend and the hotness of his mother.

Alan tries for an intimate night at a hotel with his new girlfriend, while Charlie takes a different approach to obtain the "girlfriend experience"

Charlie is visited by the ghosts of his ex-girlfriends while Alan and Jake are on a road trip.

When Jake finds out that Alan has been dating Eldridge's mom, he packs up and heads to Judith and Herb's. Meanwhile, Charlie decides it's time to cut back on boozing.

Charlie is willing to do anything for Alan to accept Lyndsey's offer to move in with her.

After moving in with Lyndsey, Alan continues to have a rendezvous with Melissa at Charlie's house.

Lyndsey and Eldridge move into Charlie's house after their home burns down.

Alan pretends to be Charlie when he goes out on the town; Charlie sneaks off for cosmetic surgery.

Charlie has difficulty dealing with dating a slightly older woman.

Charlie's girlfriend gets fed up with his stalker, Rose.

Charlie and Alan try to set up Evelyn with Russell the pharmacist.

When Berta takes a couple of days off, Charlie falls for her replacement. Meanwhile, Alan believes he's being stalked by Lyndsey's ex-husband.

When Charlie's ex-girlfriend Courtney is released from prison, he treats her to the good life despite her having been in prison for conning him.

Alan goes to great lengths to be able to get Lyndsey a nice birthday present.

Depressed after his breakup from Courtney (Jenny McCarthy), Charlie goes to see his psychiatrist (Jane Lynch).

Alan feels paranoid when Lyndsey becomes friendly with Charlie.

Obsessed and believing her to be married, Charlie starts stalking Rose. Jake and Eldridge start taping themselves doing Jackass-style stunts.

While Charlie and Rose carry on their "affair," Alan's chiropractic business turns into a Ponzi scheme.

Rose and Alan discover each other's secrets. Meanwhile, Charlie's desperate to get some time alone with Rose.

Alan and Jake meet Walden Schmidt, a broken-hearted billionaire.

Walden deals with his ex-wife, Bridget.

Alan prepares Walden for a date with Bridget, while Jake decides to emulate Walden and drop out of school.

Walden goes looking for Mrs. Right while Alan has an opportunity to reconcile with Lyndsey.

Alan has trouble accepting Lyndsey's seedy movie past, and Walden tries to cheer him up by throwing a party.

Walden receives divorce papers from Bridget, but forgets his depression when he meets a girl who looks eerily like her.

Jake has a crush on his chemistry tutor, who has a crush on Walden. Meanwhile, Alan obsesses over the journal his brother left him in his will.

When Walden begins redecorating the beach house, Alan becomes overly emotional.

Upon his release from the hospital, Alan is met with a slew of challenges that test his ability to cope.

Walden hits it off with a British babe, but neither of them is sure he's ready to re-enter the dating world.

Walden is trying his best to impress his new love interest when Bridget reappears in his life.

Walden's mother arrives and Alan is smitten with her, even as she reveals a secret about Walden's past that sends him into a downward spiral.

Walden’s ex-wife and mother try to take control of his company, so he turns to Alan for help.

Zoey tries to convince Walden to cut his hair and shave; Alan and Lyndsey revive their relationship.

Walden tries to loosen Zooey up by sharing some of Berta's special brownies.

Strained relationships and girl-fighting result when a huge storm traps Walden, Alan, Zoey and Lyndsey in the house on Valentine's Day.

Walden and Zoey's relationship suffers after they share a near-death experience. Meanwhile, Alan wonders if Lyndsey has a drinking problem.

Walden's ex-business partner shows up at the beach house looking to make peace.

Alan and Lyndsey introduce their mothers. Jake and Eldridge get a ride from Walden to a party.

Walden breaks the news to Zoey that he is going into business with his ex-wife. Alan and Lyndsey try to cope with their mom's relationship.

Walden's commitment is tested when Zoey and her daughter come to live with him. Meanwhile, Alan gets more than he bargained for when he moves in with Lyndsey

Charlie's ghost pays a visit to Alan after he suffers a minor heart attack.

Alan is showered with love and affection upon returning from the hospital, but Zoey isn’t so sure it’s deserved.

Jake is pressured to make a decision about his future.

Walden plans a big surprise for Zoey's birthday.

Zoey and Walden break up, causing Walden to experience a breakdown.

Alan and Lyndsey decide to spice things up in the bedroom.

Alan tries to find out what Lyndsey's boyfriend has over him; Walden helps Jenny pursue her acting career.

When Alan learns Walden knows Lynda Carter, he asks him to set him up on a date with her. Against his better judgment, Walden agrees to invite her to the house for dinner.

Walden and Alan find themselves on dates with two ideal women until Lyndsey's jealousy throws a wrench in their evening.

Walden goes on a date with an accident-prone model; Alan's date reveals surprising personal information about herself to him.

Lyndsey's boyfriend sets Alan up on a date; Walden wants to help Nicole with her project so she will have time to date him.

Alan finds out that Lyndsey broke up with Larry without telling him; Walden tries to prove he is a man's man.

Alan asks Lyndsey to choose between him and Larry; Jenny worries that she and Brooke are growing apart.

Walden thinks his girlfriend is cheating on him; Alan starts dating Larry's sister, Gretchen (Kimberly Williams-Paisley).

Lyndsey finds out about Alan's relationship with Gretchen; Walden has a difficult time telling Barry to find his own place.

After reconnecting with Kate, Walden becomes convinced she is the one for him -- until he meets a woman named Vivian (Mila Kunis).

Alan's girlfriend, Gretchen, insists he confess his true identity to Larry. Meanwhile, Walden goes on a road trip with Jenny and Barry to see his first car.

Alan must face the consequences after revealing his identity to Larry.

After a health scare on Halloween, Walden decides he needs to change his life.

Alan has second thoughts about getting married after he's asked to sign a pre-nup.

Alan and Walden have a meeting with an adoption social worker that hinges on them being convincing as a loving couple. Lyndsey returns after 60 days in rehab.

A birth mother considers having Walden and Alan adopt her baby.