Health services research (HSR) in pediatrics explores how healthcare systems, social factors, and policies influence access, quality, and outcomes of child health services. Pediatric care differs fundamentally from adult care, characterized by the “4 Ds”: differential epidemiology, demographic patterns, developmental change, and dependency. Evaluating pediatric services is challenging due to the rarity of severe outcomes, the predominance of preventive care, and the involvement of multiple sectors such as education and welfare. Children with disabilities represent a growing population requiring complex, long-term care and coordinated support systems. They occupy a central position in pediatric HSR, and their importance is expected to increase further in the future. This chapter also introduces a practical research example to illustrate how the author approaches study design and problem-solving in pediatric HSR. While pediatric HSR remains underdeveloped, it holds great potential to improve health systems and child well-being through integrated, multidisciplinary efforts.