This document provides an overview of theory of change approaches for evaluating social impact. It defines theory of change as describing how specific changes are expected to occur as a result of interventions and actions. The document discusses best practices for developing theories of change such as having plausible, doable, and testable causal links between activities and outcomes. It also addresses challenges such as the complexity of social systems and limitations of research available. Throughout, it provides exercises and examples to illustrate key concepts for developing and critiquing theories of change.