This document provides guidance on using causal analysis and problem trees within the Theory of Change (TOC) process. It discusses how to identify an overarching problem and draft problem statements, identify key problems and underlying causes, and represent these in a problem tree diagram. The document emphasizes the importance of causal analysis in understanding why problems exist and exploring cause-effect pathways. It also notes that problem trees help represent a systems-thinking approach to analyzing causes and effects, and that identifying strong causal linkages is critical for project design. An example problem tree is provided and analyzed to identify strong and flawed causal linkages.