A large body of literature recognizes that memory failure is a part of the daily lives of humans. Recent research suggests that similar errors may occur in animals as well. This dissertation is a multidisciplinary investigation of error in humans and animals. I first discuss the theory of error and introduce concepts used throughout the dissertation. I then present three studies of human memory failure which better define the concept of error and the methods for assessing memory in everyday life, and then use these methods to assess the association between different tasks and the possible causes of error. Next I transition into animal error, defining a framework by which error can be studied in animals and introducing a novel operant device designed for this purpose. Finally, I use this device to test the effects of motivation, distraction, and behavioral traits on performance in animals. Overall, these studies provide a start to a continuing line of cross-disciplinary research.