The Guide provides information and advice, primarily for healthcare professionals, about how to involve children in decision-making processes regarding their health. It starts by presenting the theoretical and legal context and progresses to describe important components of the decision-making process, helping health professionals to understand their role in supporting children, families, and other professionals to enact this in practice. Key concepts of consent, assent, and ‘best interests’ are discussed, as well as common healthcare situations where participation in decision-making may sometimes be perceived as more challenging. Examples and links to good practice are provided throughout.