Abstract: Sand nourishments have become a popular management option to mitigate coastal retreat for sites with abundant sand supplies. Off-site sand is placed on the dry beach or under water at typical water depths up to 10 m. This nearshore zone has a high bed level variability and contains a cascade of morphological features. This makes the understanding and forecasting of nourishment morphodynamics and impacts challenging. The emerging climate-change effects, sea-level rise in particular, call for significant progress on this topic in due time. This paper presents an overview of field, laboratory and modeling studies on nourishment morphodynamics. Four key knowledge gaps were identified. First, the spreading of nourished sand through the coastal zone is poorly understood, and has not been quantified. Second, it is unclear how design variables such as size, placement location and grain-size affect the nourishment lifetime, spreading and impact. Third, the cumulative effect of repeated nourishments on the coastal system is unknown. Fourth, models are not capable to reliably predict the morphological development and impact of nourishments. To tackle these knowledge gaps, we have launched the SOURCE research project.