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, Jake, and Charlie all decide to try new things: Alan is dating more than one woman, Charlie learns to cook, and Jake experiments with beer.

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

Charlie tries to help Jake's former teacher, who became a stripper after dating him, but things go from bad to worse when she has a religious conversion.

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 new girlfriend Chelsea asks him to spend the night at her place, which puts Charlie well outside of his comfort zone, while Alan tries to enforce a punishment on Jake initiated by Judith for mooning a group of girls.

Charlie finds himself in an uncomfortable position when Jake takes off with the daughter of a former NFL player. Charlie's Mercedes proves a boon to Alan's love life.

Evelyn offers to pay for Jake's college education, and Alan becomes listless because he has no compelling reason to work anymore, while Jake discovers a hidden talent in the culinary arts that may allow him to bypass college altogether.

Charlie finds himself re-examining his wild ways when an old friend dies and begins to feel that his time on Earth may be drawing to a close.

Charlie and Jake fight for the affections of a waitress, while Alan fights sexual tension with his receptionist.

Judith is pregnant with a baby girl and Alan is convinced he is the father.

Melissa doesn't think Alan's family appreciates him, so she asks him to move in with her and her mom.

Charlie ends up in couples counseling.

Charlie has to remove a half-naked woman from his bedroom before Chelsea arrives.

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 mourns the loss of his bachelor pad as he reluctantly allows Chelsea to move in. Meanwhile, Alan discovers there is no longer much space left in the house for him.

Alan and Chelsea become best buds, and Charlie decides to take advantage of the situation.

Charlie starts to question his relationship with Chelsea when he hears that Mia is back in town. Meanwhile, Judith goes into labor and Charlie, Alan and Herb rush her to the hospital, on the sixth season finale.

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.

Charlie is miffed over Alan's planned attendance of Chelsea's birthday party and suffers the indignity of having Jake chauffer him around following a license suspension.