This chapter, authored by Jan van den Akker from the University of Twente, explores the role of research in educational design and development activities. It is divided into two main parts: the rationale and basic principles of development research, and the methods of development research. The first part outlines the motives for conducting formative research, including the limitations of traditional research approaches in providing practical solutions for educational design problems. It also discusses the challenges faced by professional designers in dynamic contexts and the need for timely and relevant research support. Additionally, the chapter highlights the complex and ambitious nature of educational reforms, emphasizing the importance of evolutionary and interactive research approaches. The chapter also addresses the underrepresentation of educational research in policy-making and the need for more empirical evidence and theoretical articulation. The second part of the chapter delves into the methods of development research, exploring typical problems and dilemmas, and discussing challenges for further action and reflection. It aims to contribute to the emerging discourse on the principles and methods of development research in education.This chapter, authored by Jan van den Akker from the University of Twente, explores the role of research in educational design and development activities. It is divided into two main parts: the rationale and basic principles of development research, and the methods of development research. The first part outlines the motives for conducting formative research, including the limitations of traditional research approaches in providing practical solutions for educational design problems. It also discusses the challenges faced by professional designers in dynamic contexts and the need for timely and relevant research support. Additionally, the chapter highlights the complex and ambitious nature of educational reforms, emphasizing the importance of evolutionary and interactive research approaches. The chapter also addresses the underrepresentation of educational research in policy-making and the need for more empirical evidence and theoretical articulation. The second part of the chapter delves into the methods of development research, exploring typical problems and dilemmas, and discussing challenges for further action and reflection. It aims to contribute to the emerging discourse on the principles and methods of development research in education.