The attachment theory by John Bowlby deals with the effects of early childhood relationship experiences on personality development. The first part of this book presents both the historical and theoretical foundations of attachment theory in detail. The second part outlines the current state of research and future perspectives regarding the determinants, transmission, continuity, and consequences of individual differences in attachment organization. In the final part, the applicability and implementation of attachment theoretical concepts and knowledge for diagnostics, counseling, and therapy are explained from the perspective of practicing psychologists and psychiatrists.