Research teams from the Parent-Infant Sleep Lab at Durham University, UK, and the Mother-Baby Sleep Lab at Notre Dame University, USA both study mother-infant sleep behavior and night-time care-giving and utilise The Observer® Video Pro 5.0 (Noldus Information Technology bv, The Netherlands) for data capture and analysis. The research questions we address are similar, deriving from anthropological perspectives on infant care practices within an evolutionary paradigm. The Durham team have recently completed a study of mother-newborn sleep behavior on the 1st two post-natal nights in a hospital setting, while the Notre Dame researchers have examined night-time parenting behavior of adolescent and adult first-time mothers with their 4 and 8 months old infants in the setting of the sleep lab. In both studies mother-infant sleep and care-giving behavior is captured to videotape using low-light intensity cameras illuminated via infra-red light. Observation periods last for the entire night and video coding is therefore complex and prolonged. Individual behaviors and dyadic interactions (sometimes triadic in the hospital study) are coded as events or states according to similar multi-level behavioral taxonomies in both studies. We operate 11 behavioral classes with up to 14 elements per behavioral class, and 8 modifier classes with up to 20 elements per modi.er class. Behavioral recordings are of 8 to 15 hours duration resulting in data files that contain an average of 1600 observations. Simple analyses involve generating output of event frequencies and state durations per dyad (e.g. frequency of crying, duration of sleep bouts). More complex analyses of behavior sequences and time-lag analyses are also required (e.g. intensity of signalling required for baby to wake mother; time lag between baby’s first signal and maternal response). In some cases the limitations of the observation environment causes difficulty. In other cases aspects of software design thwart some of our analytical desires. This short presentation will describe our common experiences of coding and analysing nocturnal mother-infant interactions using The Observer Video-Pro