Learnability and Human Errors are influential factors of the usability of most interacting systems. This book explores the human errors and the learnability situation of authentication systems to contribute to the development of more usable interactive system. The authors investigated through observations and interviews to achieve the aim of this study. A minimalist portable test lab was developed in order to conduct the observation process in a controlled environment. At the end of the study, the authors presented the list of identified human errors and learnability issues, and provided recommendations, which the authors believe will help researchers to improve the overall usability of authentication systems.