This study investigates the influence of infant irritability, maternal responsiveness, and social support on the development of secure and anxious infant-mother attachments at 1 year. Infant irritability was assessed during the neonatal period using the Neonatal Behavioral Assessment Scale, maternal responsiveness to crying was measured during observations at 3 months, and social support was based on interviews also conducted at 3 months. Security of attachment measures were derived from strange-situation videotapes. Results indicate that social support is the best predictor of secure attachment, and that it is most important for mothers with irritable babies. Maternal unresponsiveness is associated with resistance during reunion episodes and appears to be a mechanism through which anxious attachment develops. Some evidence suggests that social support may mitigate the effects of unresponsive mothering by providing the infant with a responsive substitute. Results are discussed in terms of a transactional/contextual model of development.