This chapter discusses the role of research in educational design and development. It outlines the rationale and basic principles of development research, including motives for conducting formative research, analyzing definitions and aims of various types of development research, and discussing key characteristics. It also explores methods of development research, typical problems and dilemmas, and challenges for further action and reflection. The chapter emphasizes that education is often viewed as a 'design science,' focusing on problem-oriented and interdisciplinary approaches. While 'Design & Development Research' might be a more accurate term, 'Development Research' is used as an umbrella term due to its brevity and the common interchangeability of 'design' and 'development' terms. Development research is important because traditional research methods often fail to provide useful solutions for complex design and development problems in education. Designers need more adequate information and timely feedback to improve their work. Additionally, many education reforms are complex and require evolutionary approaches with integrated research to guide implementation. Reform efforts in education are often ambitious and multifaceted, requiring research to address complex issues and ensure effective implementation. Information and communication technology (ICT) in education also benefits from research to manage its inherent complexities. There is a need for better theoretical articulation, empirical evidence, and wider application of development research in practice. Policy makers often neglect research in favor of direct development investments, which may be due to a lack of understanding or the unclear image of development research. The chapter aims to contribute to the discussion on the principles and methods of development research.This chapter discusses the role of research in educational design and development. It outlines the rationale and basic principles of development research, including motives for conducting formative research, analyzing definitions and aims of various types of development research, and discussing key characteristics. It also explores methods of development research, typical problems and dilemmas, and challenges for further action and reflection. The chapter emphasizes that education is often viewed as a 'design science,' focusing on problem-oriented and interdisciplinary approaches. While 'Design & Development Research' might be a more accurate term, 'Development Research' is used as an umbrella term due to its brevity and the common interchangeability of 'design' and 'development' terms. Development research is important because traditional research methods often fail to provide useful solutions for complex design and development problems in education. Designers need more adequate information and timely feedback to improve their work. Additionally, many education reforms are complex and require evolutionary approaches with integrated research to guide implementation. Reform efforts in education are often ambitious and multifaceted, requiring research to address complex issues and ensure effective implementation. Information and communication technology (ICT) in education also benefits from research to manage its inherent complexities. There is a need for better theoretical articulation, empirical evidence, and wider application of development research in practice. Policy makers often neglect research in favor of direct development investments, which may be due to a lack of understanding or the unclear image of development research. The chapter aims to contribute to the discussion on the principles and methods of development research.