You know how most shows start with a definite beginning?

For example, the family moves to a new city, or the two main characters meet each other for the first time, etc.

Well that’s most shows.

Do you know of any shows that just seem to pick things up right in the middle of the characters’ lives?

Maybe my question wasn’t fully understood?

For example, The Simpsons doesn’t really have a “momentous” start. It’s not like they move to a new house or anything. Seinfeld would be another show like this. King of Queens maybe?

A show like Mad About You wouldn’t count since the two main characters meet each other for the first time. That’s a big deal.

Everybody Loves Raymond joins in progress, as its kind of "model after", Dick Van Dyke Show, did.

Both shows used subsequent flashback shows to fill in past details.

Ones I immediately think of are Leave it to Beaver, Father Knows Best, I Love Lucy, The Waltons, and Star Trek. I'm sure there are plenty of others. They don't have a special first episode; they just pick up in media res.

Kids Incorporated - originally contained an unaired pilot on how the original band was formed, but due to numerous changes that occurred when Thomas W. Lynch and Gary P. Biller became the producers after the pilot failed to sell, most notably, the removal of all the original band members except for Mickey (Jerry Sharell) and Gloria (Marta Marrero), the promotion of intended recurring characters Renee (Renee Sands) and Stacy (Stacy Ferguson) to full band members, and finally, the addition of new band member Kid (Rahsaan Patterson) and a group of backup dancers to augment the singing group members on stage and in fantasy sequences, the pilot pretty much became rendered moot, and thus the first episode largely was aired in media res, and the only "introductory episode" marking about it was that it was when Riley (Moosie Drier) became the soda jerk for the central setting, the P*lace, for the first time.

Ellen - The pilot episode consisted of Ellen trying to get a good driver’s license picture, as well as Holly going on a date with a guy the gang finds out to be slimy, so they go to rescue her.

The Odd Couple - The first episode, titled “The Laundry Orgy” showed Oscar and Felix cutting a poker game short to go on a date with the Pigeon Sisters.

Grounded for Life - There’s no first episode plot for the debut episode of this series. Just Sean catching (and throwing fried chicken at) Lily making out with Brad O’Keefe in his car.

I would not include The King of Queens because that had a first episode plot. It was where Arthur first moves in with Doug and Carrie. Also, Mad About You didn't start with Paul and Jamie meeting. In fact, that one was a flash back episode later in the first season.

THE ANDY GRIFFITH SHOW, THE DICK VAN DYKE SHOW, BONANZA, GUNSMOKE...a lot of the westerns.
Also MAD ABOUT YOU, THE SIMPSONS, FAMILY GUY...a lot of shows.