This paper presents single-subject analyses of newly developing attachment relationships in10 foster infant–caregiver dyads. Using a diary methodology, at least 2 months of dailydata were provided by foster parents on infants' attachment behaviors. Foster infantattachment was also assessed using the Strange Situation. Foster mother state of mind regardingattachment was measured using the Adult Attachment Interview. For eight infants, diary datarevealed predominant patterns of attachment behavior emerging within 2 months of placement.In most cases, diary data predicted Strange Situation classifications. Both Strange Situation anddiary data indicated that the three children placed in foster care before 12 months of age withfoster parents having primary or secondary autonomous states of mind were classified as havingsecure attachments. The five children placed after 12 months of age showed predominantlyinsecure attachment behavior in the diary and were classified as insecure in the Strange Situation.Contingency analyses of behavioral sequences reported in the diary revealed that foster parentstended to complement their foster childrens' attachment behaviors.