The pattern of ripples which we observe in the Microwave Background radiation provides the seeds of the structure which we see in the Universe today. If we measure the positions and distances of galaxies, constructing what cosmologists call a redshift survey, we see that galaxies are not uniformly distributed throughout the Universe, but are clustered - arranged in filaments and sheets, the pattern of which tells us a great deal about how such structure formed. Shown below are examples of galaxy redshift surveys, revealing clusters, filaments and voids in the galaxy distribution. The challenge for cosmologists is to understand in detail how these patterns emerged over billions of years as the Universe evolved.