ABSTRACT: The purpose of this paper is to review research literature on infant-directed singing, infant perception of music, and select components of mother-infant interaction. This review supports the idea that infant-directed singing may have therapeutic value for at-risk mother/infant pairs. Mothers around the world intuitively utilize and modify specific musical elements when singing to their infants. In response, infants show alterations in attention and arousal as well as clear preferences for their mothers' unique singing style. Furthermore, infants have sophisticated processing abilities for music stimuli, suggesting a biological predisposition for music perception. Music, therefore, provides developmentally appropriate sensory stimulation for even the youngest of infants. Through infant-directed singing, mothers and infants demonstrate reciprocal behaviors considered necessary for the development of secure attachment, including maternal sensitivity and infant affect regulation. Consequently, infantdirected singing may serve as an effective treatment intervention for mothers and infants who are at-risk for insecure attachment. The quality of the mother-infant relationship has critical implications for a child's development and later competence as an independent being. For example, a mother who soothes her crying infant by speaking in a quiet voice essentially teaches the infant how to comfort himself (Crockenberg & Leerkes, 2000). This child will later be able to understand and modify his own emotional reactions as needed. In this situation, the mother is sensitive to her infant's needs, and the infant responds by regulating his affective state. These reciprocal behaviors are considered necessary for optimal mother-infant interaction and are also evident in the musical exchange known as infant-directed (ID) singing (Trehub, 2000). The similarities between mother-infant interaction and ID singing provide a logical starting point for clinical interventions in music therapy. Some mothers and infants demonstrate asynchronous interactions; that is, the responses of one do not match the emotionality or arousal level of the other. Perhaps ID singing could provide a context for these mother-infant pairs to become better attuned with one another. In order for music therapists to effectively utilize ID singing as a therapeutic tool, a theory based on scientific evidence must first be established. The purpose of this paper is to create such a theory by reviewing and synthesizing relevant research literature. The following review will identify the unique components of ID singing, including its most salient musical elements and effects on infant behavior. In addition, the review will describe how infants perceive music and clarify the significance of these abilities. Furthermore, the reciprocal behaviors of mothers and infants during ID singing and their relevance within the mother-infant relationship will be discussed in detail. Finally, the theory will be applied to the clinical population of mothers with depression. Infant-Directed Singing: A Universal Caregiving Behavior Singing to infants is considered a universal caregiving behavior that occurs in every known human culture and has been documented throughout time (Lewkowicz, 1998; Trehub, 2001;Trehub, Schellenberg, & Hill, 1997; Trehub T Trehub, Trainor, & Unyk, 1993). In fact, some theorists suggest that singing to infants may represent one of the earliest forms of music known to man (Gaston, 1968). Prehistoric mothers most likely used simple, rhythmic lullabies to soothe infants, thereby promoting infant attention and proximity. Thus, singing to infants may have conferred some type of evolutionary advantage by promoting behaviors considered necessary for survival (Huron, 2003). Recent research has determined that infant attention appears to be maintained through the unique features of ID songs. When singing to their infants, mothers tend to emphasize specific musical elements that distinguish ID songs from other musical forms (Trehub, 2000; Trehub, Unyk, & Trainor, 1993a). …