Callista Mulder is Assistant Professor at the Reproductive Biology Laboratory, Amsterdam UMC (University of Amsterdam). She develops safe and effective treatments for people struggling with infertility, including childhood cancer survivors, men with unexplained infertility, and transgender women. Her research focuses on early stem cells that have the potential to become sperm, aiming to better understand male infertility. Callista teaches at both the Vrije Universiteit and University of Amsterdam. She is committed to sharing her research beyond academia, engaging in dialogues with the public, relevant patients, clinical professionals, and policymakers.