If the long-term benefits of public health interventions are to be realized, then ongoing program implementation or sustainability is required. Sustained implementation of public health programs, however, is a considerable challenge in complex, real-world settings. As such, understanding how to best sustain evidence-based interventions is an important area of focus within implementation science. This textbook chapter provides researchers and practitioners with the most current evidence base in sustainability research and practice, while also providing practical methods, frameworks, and tools to use when planning for, or designing, sustainability interventions and strategies. The chapter first defines sustainability and explains why it is important. The rest of the chapter presents the multi-dimensional factors that may impact sustainability and gives practitioners guidance as to how they may plan for and evaluate the sustainability of their programs. Through the use of case studies that illustrate these points, practitioners will identify how to apply sustainability frameworks, assessments, and tools in their own settings.