The importance of understanding human factors is stressed as we commence this especially important chapter. We introduce the concept of user psychology in relation to biometric identity verification, and the effect it has upon realised operational performance, noting the development of the User Psychology Index, the Biometric Operability Index and the associated User Psychology Index software utility. We acknowledge the depth of human emotions and how they may be linked directly to physiological change. Human factors such as age, ethnicity, health, disabilities and general variability are discussed in this context and several examples are given of human behavioural types and associated effects upon operational performance. We ponder the subject of inherited behaviour, acknowledging the part it plays in evolution within the natural world and align it with the human condition where a mixture of inherited and learned behaviour creates varied attitudes and behavioural types. Such behaviour is influenced partly by societal developments and we should strive to understand how and why this happens. There is a direct link between this discussion and the reality of how we are deploying biometric technology. We then move to a discussion around human rights issues and how certain fundamental rights affecting both privacy and human dignity have been seriously eroded in recent times under the pretext of national security. This leads into a warning around the provision of ethical processes with respect to the deployment and usage of biometric technology. A call is made for the creation of a Biometric Constitution as a framework within which proper guidance may be provided for both systems developers and implementing agencies as to the ethical and sustainable use of biometric technology. The Biometric Users Charter is mentioned and a first draft of a possible Biometric Constitution is provided within these pages. The relevance and scope of human factors in relation to the interaction with technology, is wider and more important than many suppose. This chapter establishes a starting point from which readers may develop their understanding accordingly.