The general aim of this thesis is to provide more insight in the role of environmental and biological factors in the development of the infant attachment relationship in the general population. In Chapter 2 the question is addressed whether maternal  lifetime history of depression and peri- and postnatal maternal depressive symptoms  are  related  to  infant-mother attachment insecurity and disorganization. Chapter 3 extends this question to infant-father dyads. Here we address the role of paternal psychopathology and sensitive responsiveness for infant-father attachment in an empirical study and in a meta-analysis. In Chapter 4, we take underlying physiological systems into account. Here we study the association between maternal depression,  infant-mother attachment quality and child autonomic functioning, re?ecting the functioning of the child’s stress regulation system. Chapter 5 examines the same association using cortisol as a biological marker of stress-regulation capabilities. Chapter 6 addresses the question whether early structural neurobiological dif ferences may predict attachment disorganization. In Chapter 7, we report ?ndings concerning the role of breastfeeding for maternal sensitive responsiveness and infant-mother attachment quality. Finally, we conducted a ?rst study examining the consequences of infant attachment quality and parenting stress for emotional and behavioral problems at 3 years of age. The ?ndings are described in Chapter 8. Against the background of our results, the determinants of infant attachment quality in the general population will be discussed (Chapter 9).