Infant-mother-pairs (N = 16) including 5 thirteen-month-olds and 11 twenty-four-month-olds participated in an experiment which examined the relationship between the amount of theory-of-mind words used by parents during book-reading and their infants? emotion recognition and understanding. The amount of theory-of-mind (e.g. emotion, desire, cognition) words mothers used during a book reading task was coded. Emotion recognition and understanding was tested using an intermodal-preferential-looking procedure developed by the researchers. The number of theory-of-mind words parents used during book-reading was positively related to infants? recognition and emotion understanding of happy and sad emotions. The results show a link between exposure to theory of mind words and emotion understanding and show how book reading is a valuable context where this exposure can occur.