The link between maternal smoking in pregnancy and asthma or wheeze in offspring is well-documented, but emerging evidence suggests that paternal smoking could also impact child health. This project aims to investigate to what extent paternal smoking in the prenatal period can causally affect childhood respiratory function, through a direct effect (e.g. via the male germline), or via an indirect intrauterine effect of maternal (passive) smoke exposure. Findings will help indicate whether or not fathers could be an effective (but currently understudied) target for interventions designed to lower the rate of childhood respiratory disorders.