Sara Bergmark Elfgren (a.k.a. Sara B. Elfgren) is an award-winning Swedish writer, screenwriter and playwright. She made her debut with the YA novel The Circle (2011), which she co-wrote with Mats Strandberg. The Circle was the first part in the Engelsfors trilogy, and it has been translated into twenty-five languages.

Since her debut, Elfgren has written critically acclaimed novels, children's books, graphic novels, audio dramas, plays, screenplays and TV scripts.

She was born in Stockholm and still lives there. She has a degree in Film Studies. She enjoys reading, watching old movies, listening to music, playing video games and going for long walks. She is currently working on an opera libretto, a new novel and a children's book.