Evaluators are often faced with many challenges in the design and implementation of a program's evaluation. Because programs are entangled in complex networks of structures and stakeholders, they can be challenging to understand, and they often pose issues of competing and conflicting goals. However, by using a systems mapping approach to evaluation design, evaluators can identify and diagram the relationships between different variables and learn about their potential impact and unintended consequences on a program's processes. In this article, we describe how using a systems approach and causal loop mapping approach during an evaluation of a demonstration program for people with developmental disabilities helped evaluators to better understand the program's implementation and the variation in the program's outcomes. (Contains 1 table, 6 figures and 2 notes.)