The last decade has witnessed impressive progress in our understanding of galaxy formation and evolution. Despite important technical and interpretive difficulties, the broad phenomenology of galaxy assembly has been described with sufficient accuracy to start constraining models of galaxy formation and evolution. The history of star formation has attacked from two complementary and largely independent angles - through the evolution of the cosmic-averaged star formation rate, and through the build-up of stellar mass with cosmic time. Prior to z ~ 1, stars formed rapidly, and ~ 2/3 of the total present-day stellar mass was formed in this short ~ 4 Gyr interval. The epoch subsequent to z ~ 1 has seen a dramatic decline in cosmic-averaged SFR by a factor of roughly 10; however, ~ 1/3 of the present-day stellar mass was formed in this 9 Gyr interval. These two diagnostics of cosmic star formation history paint a largely consistent picture, giving confidence in its basic features.
The assembly of present-day galaxies from their progenitors through the process of galaxy mergers was studied using three largely independent diagnostics - the evolution of galaxy close pairs, the evolution of morphologically-disturbed galaxies, and the evolution of early-type galaxies as a plausible major merger remnant. The interpretive difficulties plaguing all three diagnostics are acute; accordingly our understanding of the importance of major mergers in shaping the present-day galaxy population is incomplete. Yet, all three diagnostics seem to indicate that an important fraction (dare I suggest 1/2?) of ~ L* ~ 3 × 1010 M galaxies are affected by galaxy mergers since z ~ 1. This contrasts sharply with the form of the cosmic star formation history, where all of the action is essentially over by z ~ 1. It is not by any means indefensible to argue that late mergers shape the properties of the massive galaxy population in a way which is qualitatively consistent with our understanding of galaxy formation and evolution in a CDM Universe.
Yet, it is clear that much work is to be done to fully characterize the physical processes driving galaxy evolution in the epoch since reionization z 6. The `shopping list' is too extensive to discuss properly, so I will focus on three aspects which I feel are particularly important.