Jan Michel Pieńkowski is a Polish-born British illustrator and author of children's books. He is probably best known for his Meg and Mog books with writer Helen Nicoll and for his pop-up books, including Haunted House (winner of the 1980 Kate Greenaway Medal), Robot, Dinner Time, Good Night and seventeen others.

Pieńkowski illustrated his first book at the age of eight, as a present for his father. During World War II, Pieńkowski's family moved about Europe, finally settling in Herefordshire, England in 1946. He attended the Cardinal Vaughan School in London, and later read English and Classics at King's College, Cambridge.

After leaving university Pieńkowski founded the Gallery Five greeting cards company. He began illustrating children's books in his spare time, but soon found the work taking over all his time. He began working with children's author Joan Aiken in 1968; he later won the first of two Kate Greenaway Medals in 1972 for his illustrations for Aiken's The Kingdom Under the Sea.

Pieńkowski has had a life-long interest in stage design. He was commissioned to provide designs for Theatre de Complicite, Beauty and the Beast for the Royal Ballet, and Sleeping Beauty at Disneyland Paris.

In 2005 Pienkowski contracted a civil partnership with David Walser, with whom he has been in a relationship for over forty years.

Pienkowski suffers from bipolar disorder.