The document provides an overview of design-based research (DBR) and its application in a case study of the Mobile English Listening and Language Enhancement System (MELLES) project. DBR is introduced as a methodology that aims to improve educational practices through iterative design, development, implementation and analysis in collaboration with practitioners. Key aspects of DBR discussed include its flexibility, context-specificity, and focus on both theoretical and practical evolution. The document then outlines the MELLES case study, which used DBR to develop a mobile listening skills program. Implications, limitations and recommendations of DBR are also discussed.