Neutrinos and other light relic particles leave a number of imprints in the cosmic microwave background anisotropies and on maps large-scale structure of the universe. Some of these imprints can not only demonstrate the presence of these particles, but can provide insight into their nature via signatures of interactions or other behavior that changes during the history of the Universe. I will present some ideas for learning about light relics and discuss prospects for extracting information about them with future cosmological datasets.