This book examines basic knowledge in the field of infant and early childhood mental health. It focuses on cognitive, social, and emotional development of infants and toddlers and examines different aspects of neurobiological development, including genes and epigenetics as well as biobehavioral synchrony. In addition, the book addresses parenting and caregiving issues, including attachment, parent-infant relationships, and high-risk factors (e.g., the effects of trauma on the infant-caregiver relationship, adolescent parenting, and parents with substance abuse disorders).