 The study explores the benefits of co-design in developing smartphone apps using Agile methodology, which allowed for patient and care partner input to be incorporated iteratively throughout the design and development process. The co-design approach comprised end-user representation at research and software development meetings via patient proxy, equal decision-making power for all stakeholders based on their expertise, and continuous user consultation, user testing, and feedback. The study found that patient and care partner input was critical throughout the development process for early identification of design and usability issues and for identifying solutions not previously considered by the research team. This article was authored by Sarah Fox, Laura J. E. Brown, Stephen Entrabus, and others.