Julie Ellis

Julie Ellis is a New Zealand-based children's author best known for her mathematically themed picture books. She wrote What's Your Angle, Pythagoras? A Math Adventure as a way to show her daughter practical uses of the Pythagorean theorem, blending historical fiction with geometric concepts for young readers. She is credited in publishing records as Julie Ellis, 1961–, and lives in New Zealand.

Ellis has written many books for children, including Pythagoras and the Ratios: A Math Adventure, which, like What's Your Angle, Pythagoras?, is part of Charlesbridge’s math-focused picture book list and illustrated by Phyllis Hornung Peacock. Her work is frequently recommended by math education resources and literacy sites for introducing geometry and the Pythagorean theorem to elementary and middle-grade students.