Background Many but not all studies suggest an association between air pollution exposure and infant mortality. We sought to investigate whether pollution exposure is differentially associated with all-cause neonatal or postneonatal mortality, or specific causes of infant mortality. Methods and findings We separately investigated the associations of exposure to particulate matter with aerodynamic diameter � 10 μm (PM 10), nitrogen dioxide (NO 2), and sulphur dioxide (SO 2) with allcause infant, neonatal, and postneonatal mortality, and with specific causes of infant deaths in 7,984,366 live births between 2001 and 2012 in England and Wales. Overall, 51.3% of the live births were male, and there were 36,485 infant deaths (25,110 neonatal deaths and 11,375 postneonatal deaths). We adjusted for the following major confounders: deprivation, birthweight, maternal age, sex, and multiple birth. Adjusted odds ratios (95% CI; p-value) for infant deaths were significantly increased for NO 2 , PM 10 , and SO 2 (1.066 [1.027, 1.