What is a Theory of Change? There is no agreed definition on what a Theory of Change is. Theories of Change are essentially about how we think that change happens. It is nearly always a mix of evidence and assumptions. If a project involves people, then it will inevitably mean theories about power transference, behavioural economics and norms, etc. We often carry these theories around implicitly in our head, no longer questioning causalities that may or may not actually hold up. Most people point back to Carol Weiss as being the person who formulated the concept of ToCs for this sector.i Weiss described a Theory of Change as “a theory of how and why an initiative works.”ii