Title: Galaxy Clusters: Cradles of Galactic Civilization Abstract: Galaxy clusters are the largest, most massive structures in the Universe, each containing hundreds of gravitationally-bound galaxies. They are the first large-scale structures to form after the Big Bang, produce the bulk of the stellar mass ever created, and are powerful probes of the cosmological parameters that describe the past and future dynamical evolution of the Universe. Individual galaxies within clusters reside in an extremely harsh environment, consisting of million degree plasma and copious amounts of dark matter, and in their younger days they experienced frequent "train-wreck" mergers with other galaxies. Although great strides have been made in recent years in understanding typical galaxies, any successful model of galaxy evolution must also explain the extreme lives of galaxies in clusters. I will highlight some recent work that has at last revealed the era of peak star formation and black hole activity in galaxy clusters and will describe ongoing work to push our understanding to the next level. **Refreshments will be served at 2:15 p.m. (BEFORE the seminar) in room ARC 233