Interactive wearable devices---or wearables---are increasingly being used to track the health-related data of their users. The design of such systems is a considerable challenge that stresses the analysis and design techniques of software engineering and human-centered computing and places considerable demands on user experience designers to produce systems that are reliable, accurate, and understandable while also remaining customizable by end users. In my work, I aim to address this situation by developing a design framework that can be used to organize the activities during the development life cycle of a health-related wearable system. The WISE framework proposes a set of heuristics, activities, and principles by which health-related wearable systems can be both designed and evaluated. To demonstrate the power of my framework, I conducted five studies to help design the user interface of a wearable system that helps users visualize their heart rate data and monitor that data for anomalies that may require the attention of a medical professional. Over the course of my five studies, the principles of the WISE framework helped me design visualizations that are easy to understand by users and provide them with value in terms of being able to communicate with their doctors about the health of their heart. To illustrate the generic nature of my framework, I have also demonstrated how my framework could be used to design health-related wearable systems that monitor other medical conditions such as depression and Parkinson's disease.