A special session titled 'Complexity in Modeling: How Much is Too Much? was convened at the 2011 Geological Society of America Annual Meeting. The session had a variety of thought provoking presentations-ranging from philosophy to cost benefit analyses-and provided some areas of broad agreement that were not evident in discussions of the topic in 1998. Complexity will not go away simply by fiat; too many problems require complexity to adequately address societal needs and expectations. Fred Molz expanded the philosophical underpinnings of model complexity with an example of 'computer-aided thinking.' This term suggests a utility for models even if mathematical chaos violates the concept of a single unique reality or where a premise of classic model prediction fails. Daniel Abrams compared end-extremes of the complexity simplicity scale, where insights gained from intensive particle tracking from a 3-D groundwater flow model were also obtained using a simple exponential solution for predictions of watershed scale transit time distributions.