A character, usually female, suspects a male character, often a neighbor, of committing a crime. Perhaps she is even a witness of the crime. Nobody believes her, or she isn't sure herself, so she decides to wait until he leaves his house, and then sneak in to look for clues or to obtain incriminating evidence. Of course, the potential suspect will invariably come home early, and the investigating character will have to find a way out of the house without being discovered. Sometimes they do, sometimes they don't.
This can be an Idiot Plot, because the character in question often fails to be certain that the probable bad guy will actually be gone for a while and is not just getting his mail or something. In some versions, another character will be placed as a lookout, but they will either become distracted and fail to notice the bad guy as he arrives home, or their signal to get out will go unnoticed by the infiltrating character.
There's also a less common but still prevalent comedy version of this trope, where the investigating character is trying to retrieve something, often an embarrassing item they've left behind.
Compare Alone with the Psycho, The Stakeout.
Brian De Palma's Sisters is in part a homage to Rear Window. The variation is that the suspect is female rather than male, and the character snooping in her apartment is male. Interestingly, each character has an opposite-gender accomplice.
This is a crucial part of the English folktale, Mr Fox. Lady Mary, Mr Fox's intended bride, is suspicious of him and follows him home to see his castle for herself - and gets more than she bargains for when she finds the literal skeletons in his cupboards. A ballad version by the folk group Mr Fox has the girl bring home evidence of her encounter with Fox's latest conquest and confront him with it:
Foxy took his knife
And with a blow both sharp and sweet
The hand was severed from the wrist
And dropped down at my feet
Foxy turned his back on me
He turned as if to leave
But I took him by the arm and plucked
The hand from out my sleeve
Older Than Radio: Occurs in Jane Austen's Northanger Abbey where after reading too many Gothic novels, the heroine begins to mistrust her host General Tilney and suspect him of murdering his wife years before. This novel actually predates Rear Window by almost two centuries.
In The Lovely Bones a girl breaks into her neighbor's house to look for incriminating evidence in the death of her older sister.
In Dirk Gently's Holistic Detective Agency, one of the main characters breaks into his girlfriend's house to delete a message from her answering machine (Note: the book being written and set quite a while ago, this means listening to all of her messages, off a series of cassettes, until he finds the one he made). It turns out he's actually possessed by an ancient alien ghost.
An RL Stine clearly and deliberately rips off the plot of Rear Window when a young woman accompanies her friends on a ski trip and ends up spraining her ankle. Stranded in her room and bored, she begins spying on the other cabins with a pair of binoculars. Sure enough, she witnesses a murder and the killer him/herself, though she can't tell who it is—it quickly doubles as a Locked Room Mystery when she realizes it has to be one of the friends she's traveling with—and ends up playing a nail-biting cat-and-mouse game trying to figure out exactly who it is without tipping them off.
Live Action TV
The Seinfeld episode "The Phone Message" revolves around an angry message George left on his date's phone while she was out of town, and his attempts, using Jerry as a decoy, to sneak into her living room and change the cassette before she hears it. She reveals later that she had had her friend play her the messages and took George's tirade as a dry joke, their successful effort to switch tapes a waste of time.
The Monk episode "Mr. Monk, Private Eye" contains a unique version of this trope, in which Monk sneaks on to Jay Bennett's yacht and is promptly stowed away.
Done ad nauseum in Psych, wherein Shawn has ended up stowed on a boat, caught sneaking around various facilities (including a Seaworld-like park after-hours), and too many others to count. The sheer number of times he has snuck into someone's property means that, statistically, he should still be paying fines/jailtime for breaking and entering by 2099.
In a Halloween episode of That '70s Show, Fez breaks his leg and stays in Eric's room, watching the Pinciotti's house and hoping to see Midge, their MILFy next door neighbor, naked. However, when she's nowhere to be seen and her husband Bob is seen by Fez carrying a large, bloody bag, Fez immediately assumes that Bob killed Midge. It turns out that Bob had merely butchered a cow and Midge was away on vacation.
The episode of Castle, "The Lives of Others", plays this trope exactly straight - Castle is so bored while recovering from an accident, that he starts watching his neighbors through binoculars, and sees what is clearly a man murdering his girlfriend with a knife. When Beckett doesn't believe him (she even calls it a "rear window scenario"), he posts Alexis to be his watch while he breaks into the neighbor's house to retrieve some evidence - except he's still on crutches, falls over when he tries to leave, and has to hide under the bed. Turns out it wasn't played straight at all: Beckett staged the whole thing as a birthday present to Castle, and everyone, including the "murderer" and "victim", were in on the prank.
Madison gets into this predicament in "The Taxidermist" DLC for Heavy Rain
The Foster's Home for Imaginary Friends episode "Neighbor Pains", where Bloo has to go into Old Man Rivers house to look for the adoption forms that Rivers took. The papers he brings back turn out not to be the forms, but love letters to Madame Foster, which Mac and Bloo use to blackmail Rivers into giving them the forms.
Parodied in The Simpsons episode "Bart of Darkness". Bart, injured from an accident diving into their swimming pool, overhears a scream from the Flanders house, and witnesses him burying something in the backyard. Believing Ned had murdered his wife Maude, Bart orders Lisa to go investigate. When Ned returns home early, Lisa gets trapped in the attic with Flanders, who is attempting to put away an axe (though from Bart's view it appeared Ned was threatening Lisa with the axe). It later turns out that Maude is alive, and was away at Bible camp the whole time. The scream that Bart heard earlier? It was Flanders.
An episode of Rocko's Modern Life dealt with Rocko thinking Bev Bighead killed her husband Ed so he goes into their house to investigate, as it turns out Ed went to the hospital to remove a wart, the stabbing was Bev making a sculpture of Ed, and she buried a dead plant.
An episode of The Flintstones dealt with their new neighbor apparently killing his nagging wife and Fred and Barney go to investigate; at the end he tells them she went on vacation, but in a subversion he reveals to the audience that he indeed did kill her as he fed her to his wife eating bird.