This book provides a transformative approach to the understanding of mental health in the 21st century. It does so by encouraging the replacement of traditional subjective techniques with more precise and objective measures that are designed to discover individual differences in our patients. Just as in personalized medicine, where diagnostic and treatment techniques are becoming more targeted toward the specific conditions of a particular patient, so to in the mental health field we need to develop targeted and focused methods through the use of clinical science concepts and through the adoption of an agnostic, unassuming posture where the presentation of each patient is viewed as unique. For example, treatments may draw from an integrative approach that incorporates genomic and epigenomic analyses of the patient to inform a more targeted medication regimen or psychotherapy approach (some psychiatrists are beginning to use genomic analysis to aid in the choice of a specific antidepressant, for example, that would most likely be effective for a certain patient). Diagnostically, paper and pencil questionnaires leading to current diagnostic labels, long the standard, must be replaced, for the most part, by objective measures of stress that prioritize "reports from the body". Additionally, research methods of extremely complex psychological disorders can be enhanced by breaking them down into smaller subtypes (or endophenotypes) versus large phenomenologically-based symptom clusters (i.e. DSM diagnoses). Individual differences, a consistent focus throughout the book, may be the product of genetic variants and/or epigenetic mechanisms. The latter mediate gene X environment interaction that is now the primary paradigmatic lens through which we investigate and seek to explain resultant behavioural profiles. A major focus of the book is on the effects of early adversity, particularly trauma, and how they contribute to a "re-programming" of the brain through epigenetic alterations of gene expression. This results in increased vulnerability to possible psychological disorders, such as various anxiety conditions, depression, and character disorders which may manifest later in life. By identifying the epigenetic effects caused by early stressors, that is, how gene expression is altered, we can eventually make significant advances in primary prevention. This book represents an attempt to move us into a transitional domain and beyond, where causes and the treatment of psychological disorders are re-conceptualized through our developing insights from neurobiology, genetics, and epigenetics.