Francesca Lia Block (born December 3, 1962) is an American writer of adult and young-adult literature. She is best known for writing the Weetzie Bat series, which she began while a student at UC Berkeley.

Block was born in Los Angeles on December 3, 1962. Her mother was the poet Gilda Block (nee Klein) and her father was the screenwriter and painter Irving Block. She attended North Hollywood High School and the University of California, Berkeley, and later studied for her MFA from the University of California at Riverside.

Block writes both novels and poetry. Her first two books, Moon Harvest (1978) and Season of Green (1979), were small-press illustrated poetry collections, now out of print. Since then, she has released several standalone collections of poetry, as well as incorporating poetry and lyrics into many of her novels. She has published over 40 books.

Block did not originally start out with an editor, but was published by using her connections. She attributed her success partly to publishers being interested in shorter books.

In 2014, Block was named Writer-in-Residence at Pasadena City College. Block is a member of the Authors Guild, Authors League of America, and the Writers Guild of America.

In 2018, it was confirmed that Weetzie Bat would be produced as a feature film, with Justin Kelly attached as director. Block wrote the screenplay for the film.

Block is known for her use of imagery, especially in describing the city of Los Angeles. One New York Times Book Review critic said, "Block writes about the real Los Angeles better than anyone since Raymond Chandler."

Block has taught creative writing at the University of Redlands, UCLA Extension, and Antioch University.