This work addresses the importance of vitamin D sufficiency for respiratory health throughout the life course and the immune mechanisms that underpin this. This includes (i) how vitamin D sufficiency in human pregnancy may reduce asthma risk and impact the immune profile of the newborn; (ii) the capacity of vitamin D to promote lung health in adults by its impact on pathways linked to immune tolerance as well as through modifying the response to glucocorticoids in patients with chronic respiratory disease; and (iii) the capacity of vitamin D to protect against the detrimental effects of particulate matter air pollution.