The present study examined the assumption that emotion-related characteristics of mothers and infants contribute to the development of infant-mother attachment in the first year of life. Mothers' emotion and personality characteristics were assessed with expressive-behavior ratings and self-report scales. Infant characteristics were measured by emotion and temperament questionnaires (mother report) and objective coding of facial expressions of emotions. Attachment classifications were determined by means of the Strange Situation procedure, and a continuous-variable index of attachment security was derived by a discriminant function procedure. Mothers' emotion experiences, expressive behaviors, and personality traits were significant predictors of the level of security of the infant-mother attachment. Infants' expressive and temperamental characteristics as rated by their mothers were also significant predictors of attachment security.