Strong gravitational lensing (SL) is nowadays at the very heart of important issues in modern cosmology, allowing for instance to map the dark matter distribution of galaxy cluster’s cores, to detect very high redshift sources or to constrain the geometry of the Universe.

I will present the most recent results from the Reionization Lensing Cluster Survey (RELICS) which has targeted 41 cluster fields to efficiently look for high-z galaxy candidates (z ~6 to 8). We have used a semi-parametric pipeline (LTM) to map the dark matter distribution of several clusters and characterise the properties of background high-redshift galaxies that can help probe the reionization epoch with future follow-up observations. Some of these clusters have been found to have particularly large Einstein radii making them powerful tools to place useful constraints on structure formation and cosmological models.