The largest features of the largest structures

In the hierarchical paradigm of large-scale structure formation, galaxy clusters are the largest objects ever to virialize. These island universes are thought to grow by accreting mass through surrounding large scale, strong yet elusive, virial shocks. After reviewing our understanding of structure formation in the Universe, I will describe the hunt for these virial shocks. I will argue that a combination of analytical, numerical, and observational techniques has recently led to the first detections of these shocks, thus providing new routes for studying large-scale structure, tracing the cosmic-web, constraining shock physics, and probing dark matter and dark energy.