It is my amateur-theatrics life dream to direct this. Someday…
A tv series that pops to mind is “Smash”, from 2012, which is behind the scenes fictional drama about launching a Broadway musical based on the life of Marilyn Monroe. I never quite got around to finishing season 1, but I did enjoy what I saw of it.
Wow, you’ve been IN it? What part did you play?
<ThelmaLou gazes at you, starry-eyed…>
A few years ago, I saw Patrick Stewart on Broadway starring in A Life in the Theater, a comic play by David Mamet about two actors with a small, not very successful theater company.
Springtime for Hitler.
Was it funny? I heard a lot of negative word-of-mouth about it at the time, though I admit it had slipped my mind until now.
I was Selsdon in a college production. It was quite possibly the most fun I’d ever had in a show. Just the word sardines makes me crack up like no other.
There’s a novel by Garson Kanin also called Smash, from 1980.
It’s also about the making of a fictional Broadway musical, although not about Marilyn Monroe, It’s a lot of fun.
The best Discworld novel about the theater is Maskerade, which is his take on Phantom of the Opera, and is better than Wyrd Sister (although also about the witches).
Interested in children’s books about the theater? I recommend Ballet Shoes, Theater Shoes (its sequel) and Dancing Shoes, all by Noel Streatfeild.
I can see that! What a great memory. 
I think they made a movie too with Jack Lemmon and Matthew Broderick
A Double Life (1947) stars Ronald Colman as a Shakespearean actor who has trouble distinguishing his real life from the character he plays. It’s not one of my all time favorites but I thought it was very good and sadly underappreciated today. Colman won his only Oscar for this film.
For a change of pace, there’s Shadow of the Vampire, a movie about the filming of the classic vampire film Nosferatu. The lead actor Max Schreck, played by Willem Dafoe, takes the role of the vampire Count Orlock just a little too seriously…or does he?
Sounds great! Love Dafoe.
If opera counts as theater, there’s Ariadne auf Naxos
All That Jazz, based loosely on the life of Ray Fosse.
Reuniting Michael Caine and Christopher Reeve from Deathtrap, which also counts.
I should add: Watching the original silent film Nosferatu isn’t necessary to enjoy Shadow of the Vampire. But if you do you can more greatly appreciate Willem Dafoe’s acting as well as his makeup job. And since Nosferatu is old enough to be in the public domain, there are dozens of versions floating around for free on the Internet.
THEATRE OF BLOOD. Vincent Price is an over-the-top Shakespearean actor who (a) despises the critics who despise his acting, but (b) really loves being in character.
On a totally unrelated note, Shakespeare sure loved writing unhinged killers.
Cabaret is about the life of some sleazy cabaret performers in Germany just before WWII.
*******SPOILER ALERT********
Victor/Victoria is about a fake drag queen (“he’s” really a woman) and his theatrical career, with many scenes of rehearsal, performance, and backstage antics.
A Midsummer Night’s Dream is another Shakespeare play that contains a play.
There are several Judy Garland/Mickey Rooney “let’s put on a show! we can have it in the barn!” movies. Many are sadly marred for future generations by some blackface segments.
There’s also a film called Everybody Sing about a stage family with Judy Garland and Fanny Brice, also sadly marred by a blackface scene by Garland.
The there’s Gypsy.
Shadow of the Vampire, a great film in it’s own right, may have been inspired by the success of the movie about the life of Ed Wood which included material about the filming of several of Wood’s films, with quite a lot of screen time devoted to Plan 9 from Outer Space.