From the Mixed-Up Files of Mrs. Basil E. Frankweiler

From the Mixed-Up Files of Mrs. Basil E. Frankweiler is a children's novel by E. L. Konigsburg. It follows siblings Claudia and Jamie Kincaid as they run away from home to the Metropolitan Museum of Art in New York City, and it was published by Atheneum in 1967.

It was the second book published from two manuscripts that Konigsburg, then a new writer, submitted to the editor Jean E. Karl. The novel opens with a prologue that takes the form of a letter from Mrs Basil E. Frankweiler addressed to her lawyer, Saxonberg, with a drawing of her writing at her desk, and the letter serves as a cover note for the narrative that follows while also explaining changes to her will.

Claudia's plan is to run away somewhere comfortable rather than somewhere dangerous, and the museum supplies both a hiding place and a problem, since the children have to manage money, laundry and concealment inside a public institution. The motif the book is remembered for is that Claudia wants the experience to change her, which turns an adventure about hiding into an argument about how a person becomes different from the one she was.