Infants have definite personality characteristics from birth onward. Despite wide variation in infant temperament styles, ranging from easy to difficult, responsive parents and non-parental caregivers can ensure positive emotional-social development. This paper, which reviews various theories and research on personality development in infants and toddlers, begins with a discussion of self-esteem and the caregiver's role in early childhood. The next section investigates the role of temperament and the importance of caregiver understanding of an infant's basic temperamental type (easygoing, difficult, slow to warm up). Three infant personality theorists and theories are examined next, including: Erikson and the well-regulated infant/toddler personality; Mahler and the infant/toddler separation/individuation struggle; and attachment theorists and intergenerational personality effects. The paper next explores parental sex role stereotypes and their influence on infants. Finally, prosocial development is addressed. The paper concludes that the road to positive personality development in infancy begins with competent caregivers, and that secure emotional attachment to a caregiver is important for positive mental health, including high self esteem, cooperation and compliance with adult mentors, and prosocial rather than aggressive response patterns. Contains 38 references. (SD)