Prior to expressing language, infants have mastered many means for engaging in referential communication with others. This contention can be supported by reference to (1) developmental changes in the attentional structure of communication and (2) infants' use of affective expressions as they begin to master referential communication. In an effort to document communication development in infants 6 to 18 months of age, over 56 hours of videotapes were made in the homes of 28 subjects. Infants were observed in three playing conditions: alone, with mother, and with a familiar same-age peer. Three coding schemes were formulated to describe infant expressions, document infant attention, and detail the mother's actions. Results of coding focusing on infant attention and affect indicate that, regardless of the infant's partner, affective expressions become increasingly shorter with age, and coordinated joint engagement (an attention state in which the infant shares a mutual object-focus with a partner and attends to that partner's interpersonal moves) is achieved quite late in infancy. These and other results are discussed. (RH)