Using survey data, we identify a variety of factors that influence tipping behavior and in the process lay out a simple theoretical framework to help to interpret our empirical observations. We first investigate the efficiency of observed tipping behavior. While there are elements of efficiency — notably, percent tip depends on service quality — it does not appear fully efficient. We then posit a model in which customers trade off material well-being against disutility from not adhering to the norm, and we use this model to reinterpret initial empirical findings and make additional empirical predictions.