Antenatal corticosteroids (ACS) for acceleration of fetal lung maturation in women at risk for preterm birth are a cornerstone of feto-maternal medicine. However, more than 50 years after the first publications, there is still a number of question on best treatment: when to start, optimal interval between treatment and delivery, dose and regimen, substance and risk-benefit-ratio in special populations. We aim to shed some light on current knowns and unknowns.