Building sustainable programs, platforms, and digital tools are essential to maintain user and stakeholder support, as well as to maximize long-term impact. Sustainability ensures that user and stakeholder contributions are not minimized due to interruptions, such as a loss of funding. A program built for sustainability is more likely to be embedded into policies, daily practices, and user workflow. For many digital initiatives, institutionalization by a nongovernmental organization, private company, or local government is the ultimate goal in achieving a long-term, positive impact. For others, institutionalization is achieved by developing a business model that has sustainable revenue generation. This guide details how social impact organizations can build and maintain sustainable digital programs and initiatives.