''From the Mixed-up Files of Mrs. Basil E. Frankweiler'' is a 1968 novel by the children's author Creator/ELKonigsburg, who won her first UsefulNotes/NewberyMedal for it.

Eleven-year-old Claudia Kincade is feeling underappreciated by her parents and the world in general. The best way to teach them a lesson, she decided, is to [[TheRunaway run away from home for a while]]. But what she hates more than being underappreciated is being uncomfortable, and so she chooses to run away to the Metropolitan Museum of Art in UsefulNotes/NewYorkCity (for all those poofy Marie Antoinette beds to sleep in) and drags along her nine-year-old brother Jamie (for his $24.43).

Thus begins the adventure of a lifetime for both of them, between hiding from museum security in the bathroom, doing laundry, and scrounging for change in the museum fountain, Claudia becomes obsessed with a statue sold to the museum for $225 that may or may not be a Creator/{{Michelangelo|Buonarroti}}.

And why is the eccentric multi-millionaire Mrs. Basil E. Frankweiler writing such a long letter to her dear lawyer Saxonberg?

!!This story provides examples of:

* BigFancyHouse: The Frankweiler mansion. Claudia is particularly impressed by the bathtub.
* BrotherSisterTeam: Claudia and Jamie
* CardSharp: How Jamie acquires all his loot.
* CatchPhrase: Jamie's is "Oy, baloney!" [[spoiler: Turns out to be helpful for Claudia to remember the city of ''Bologna'', Italy]]
* TheConfidant: [[spoiler: What Claudia becomes for Mrs. Frankweiler, to both their benefits.]]
* CoolOldLady: Frankweiler, who is so old and rich and lacking in fucks to give that she amuses herself by setting the Metropolitan Museum of Art on a wild goose chase simply so she can watch the fun from afar [[spoiler: and then gives the invaluable secret of the statue to a twelve-year-old girl she's only met once solely on the basis of recognizing a kindred spirit.]]
* EccentricMillionaire: Frankweiler, she sells a [[spoiler:genuine]] Michaelangelo to the Met for pocket change then refuses to provide authentication just so that she can watch the curators squirm.
* EpistolaryNovel: The entire book is a single long letter from Frankweiler to her lawyer.
* FancyCamping: Claudia's reasoning for choosing the Met is that she wants to run away somewhere clean and comfortable.
* FreeRangeChildren: Police and journalists' reaction for missing children is really muted in the 1960s compared to today.
* GrammarNazi: Claudia has a bit of a habit of correcting her brother's grammar.
* LongTitle: ''From the Mixed-up Files of Mrs. Basil E. Frankweiler''. Creator/ELKonigsburg is fond of such titles in general.
* MiddleChildSyndrome: Claudia's sick of being lost in the middle of her family. She just wants to feel special.
* TheRunaway: Claudia and Jamie
* SenselessViolins: Claudia and Jamie packs most of their clothes in a viola and trumpet case.
* SwissCheeseSecurity: The Met overnight security.
* UnusualEuphemism: Jamie's favorite minced oath is "BALONEY", which provides Claudia the EurekaMoment required to solve the Michaelangelo mystery.