Understanding the largest physical structures in the universe is essential for the comprehension of the cosmos as a whole. We want to know how our world is formed, what it is made of and how it evolves. Galaxies, as the most visible constituents of the universe are interesting probes for the cosmic time sequence. Their formation and development provides us with unique clues to the cosmic evolution. This is tightly connected with the hierarchical cosmic structure: groups and clusters of galaxies and their embedding into the large scale structure offer the opportunity to study the dependencies. Galaxy redshift surveys delineate most impressively a large cosmic web, which is composed of sheets and filaments. Grand simulations of the cosmic evolution complement these observations from the theoretical side and allow one quantify and compare various model universes. Quasar absorption line studies, gravitational lensing and even the X-ray background radiation provide important quantitative measures of the history of matter clustering. Finally, the microwave radiation traces very early structures, which are supposed to originate in the phase of inflationary expansion shortly after the big bang. This volume constituting the proceedings of the 12th Potsdam Cosmology Workshop, deals with the basic aspects of cosmological structure formation on the largest physical scales.