Infant sleep is a major source of concern for many parents. The aims of this longitudinal study were to assess: (a) the development of sleep patterns among infants, (b) the development of maternal cognitions regarding infant sleep, and (c) the relations between these domains during the 1st year of life. Eighty-five mothers were recruited during pregnancy and completed a questionnaire aimed at assessing maternal sleep-related cognitions. After delivery (at 1, 6, and 12 months) sleep was assessed using actigraphy and sleep logs, and maternal cognitions were reassessed. The findings demonstrated significant predictive and concomitant links between maternal cognitions and infant sleep. Maternal soothing behaviors mediated the relations between these domains.