By 18-24 months of age, infants whose caregivers talk to them more tend to recognize and comprehend common words relatively quickly and accurately. In turn, real-time language comprehension skill at this age is linked to language development later in childhood. Critically, infants begin to comprehend common words as early as 6-9 months of age, but it is unclear whether the origins of lexical comprehension skill are likewise influenced by hearing child-directed speech. Instead, ambient speech, including caregiver speech that is overheard by infants rather than directed to them, may play strong supportive role in very early language development. Thus, we tested how aspects of the home language environment (HLE) are related to performance on a lexical recognition task in 9-month-old American-English learning infants (