New health care devices, including at-home diagnostic devices, are generating and aggregating data on patients’ health at a staggering pace. Yet much of that data is inaccessible because it is held in data siloes, most often cloud services controlled by device manufacturers. This proprietary siloing of patient data is problematic from ethical, economic, scientific, and broad public policy perspectives. This chapter frames these concerns and begins to sketch a regulatory framework for patient access to health care device data. As with other consumer data, breaking down siloes and securing patients’ access to their device data safeguards patients’ ownership interests, promotes patients’ ability to maintain and repair their equipment, and encourages interoperability and competition. Yet, data access is especially important for health data: It allows patients to make informed decisions about their own care, and it enables motivated citizen-scientists to study their own conditions and innovate in response to them. Patient access to device data may also be a first step toward building publicly accessible, responsibly governed datasets of so-called “real-world evidence” – which are increasingly essential to validate the accuracy and reliability of current diagnostic devices – and to invent and validate future devices, drugs, and other precision medicine interventions. These interests motivate the development of our proposed framework. Drawing from related experiences with clinical trial data and electronic health records, this chapter identifies the key considerations for a framework that protects key interests, such as privacy and data security, while unlocking the benefits of broader data sharing.