Our genomes contain vast amounts of DNA that remains poorly understood. A recent arrival on the scene of genomic “dark matter”: micropeptides, tiny proteins coded by tiny genes that had long escaped notice due to their size but that appear to be present in large number in our genome and that of every other living thing. These small molecules likely play roles in many different biological processes; scientists are recently uncovering their influence in several different diseases and in the function of the immune system. Scientists in this group are shedding new light on how micropeptides influence immunology, in health and in disease.