Implementation support practitioners are professionals who support organisations, leaders and staff in their implementation of evidence-informed practices and policies. They identify, contextualise and improve the use of evidenced implementation strategies in a range of settings. They also build implementation capacity among teams, organisations and systems. This guide identifies the competencies that implementation support practitioners need to support effective implementation and scaling of evidence-informed practices, programmes and policies, to improve outcomes for people and communities. One reason this guide is useful is that competencies for implementation support practice can be integrated into higher education curricula and training for social work and health care, certificate programmes for professionals working in human services, and ongoing professional development for leaders and practitioners charged with supporting the use of evidence to improve population outcomes. It should be of use to anyone interested in developing the competencies of professionals who are facilitating and supporting the implementation of changes in service delivery. It is designed as a tool for reflection, allowing people to have conversations about the competencies that are fundamental to implementation support practice. [This guide was co-produced by the European Implementation Collaborative and the Centre for Effective Services (Ireland).]