This book deals with the underlying issues associated with Personnel Security Vetting. It provides the rationale as to why certain behaviors are thought to have value in the process and others do not. The environment is largely that of the national security arena but much of the material can be extrapolated to the private sector. Various levels of vetting are linked to risk levels i.e. how important are certain assets to protect and how much in resources is the company willing to invest to protect those assets. The methodologies typically used (background investigations, polygraph and interviewing techniques) are dissected and decisions as to which to employ are explored. In the final analysis, decisions in Personnel Security vetting are risk/benefit determinations dependent on the mix of circumstances present at the time. Probabilities, percentages and environmental limitations are some of the ultimate determinants in the decision making process and recognition is given to the notion there are no perfect vetting measures.