This chapter focuses on design and development research, a type of inquiry unique to the instructional design and technology field dedicated to the creation of new knowledge and the validation of existing practice. We first define this kind of research and provide an overview of its two main categories—research on products and tools and research on design and development models. Then, we concentrate on recent design and development research (DDR) by describing 11 studies published in the literature. The five product and tool studies reviewed include research on comprehensive development projects, studies of particular design and development phases, and research on tool development and use. The six model studies reviewed include research leading to new or enhanced ID models, model validation and model use research. Finally, we summarize this new work in terms of the problems it addresses, the settings and participants examined, the research methodologies employed used, and the role evaluation plays in these studies.