Disabilities occur at the connection between bodily functions and structures of the person and the interacting social and physical environment. Disabilities call for understanding how interventions designed for the general population might impact differently on those with a range of different impairments within various social, historical, and environmental contexts. Monitoring, Evaluation, and Accountability (MEA) is recognized as fundamental to the achievement of the SDGs and implementing programs that ensure development resources reach the poorest in the most efficient ways. In programs for people with disabilities and the marginalized, MEA is critically important to understand the impact that programming is making and to ensure that empowerment, equality, inclusion, and the principles of human rights are being delivered through the program. The collective understanding of MEA is evolving. There are now broader interpretations of MEA, with the changes from a predominance of a legislative top-down view of MEA to a conceptual understanding and application in which MEA has a broader purpose and is used for accountability not just to a legislative body accountable to those affected by a program, and is used for decision-making for improvement as well as to report on results after their completion. This chapter provides an overview of MEA concepts and introduces and explains the most commonly used MEA tools. As well as being relevant for organizations and those involved with people with disabilities, the introduction, overview, concepts, and tools section is also relevant for anyone interested in measurement and how to demonstrate impact in social and rights-based areas. As shown in the examples of tools and guidance documents included in the user guides and tools sections, MEA management and assessment tools have been designed to support different types of organizations, including a range of different stakeholders, such as civil society organizations, governments, and development organizations.