This article reports on the use of design-based research (DBR) in the development of online reading materials for beginning and intermediate Spanish learners. The report focuses on four studies of two main aspects of the development, namely, interface design and learner perceptions. The discussion of interface design includes the analysis of learner expectations and interface organization. The analysis of learner perceptions includes frequency of use and impact of multimedia glosses on the learning of vocabulary. Findings reveal the importance of involving learners in all aspects of materials design and development and make evident the strengths of a DBR approach to the research and development of instructional materials for language learning.