Infants Growth and Development Caregiver touch plays a vital role in infants’ growth and development, but its role as a communicative signal in human parent infant interactions is surprisingly poorly understood. Here, we assessed whether touch and proximity in caregiver-infant dyads are related to neural and physiological synchrony. We simultaneously measured brain activity and respiratory sinus arrhythmia of 4 to 6 month old infants and their mothers (N=69 dyads) in distal and proximal joint watching conditions as well as in an interactive face-to-face condition. Neural synchrony was higher during the proximal than during the distal joint watching conditions, and even higher during the face to face interaction. Physiological synchrony was highest during the face-to-face interaction and lower in both joint watching conditions, irrespective of proximity. Maternal affectionate touch during the face-to-face interaction was positively related to neural but not physiological synchrony. This is the first evidence that touch mediates mutual attunement of brain activities, but not cardio-respiratory rhythms in caregiver-infant dyads during naturalistic interactions. Human development is driven by social interactions. From early on, infants begin to actively seek information as embodied agents in their social interactions. These exchanges are essential for infants’ developing understanding of self and others. In these interactions infant and caregiver typically fluctuate between aligned and misaligned states. Temporally aligning with another person facilitates mutual prediction and allostasis Regards John Editorial Assistant Clinical Pediatrics: Open Access