Ecological investigations rely on data describing the biomass, diversity, and composition of living things. In the case of microbial communities, these data are primarily gathered using microscopy and molecular genetic approaches. The diminutive size of viruses means that obtaining genetic material sufficient for molecular approaches for examining the diversity and composition of aquatic viral assemblages can be challenging. Moreover, in procedures for the isolation and cultivation of novel viruses from natural waters, high-density viral inocula provide the best chance for success. To address the need for samples containing a high-density of viruses, investigators have used tangential-flow filtration (TFF) to concentrate viruses from large-volume (>20 L) water samples. This report outlines procedures for the preparation of viral concentrates from large volume water samples using TFF and discusses the effect of concentration procedures on viral recovery and downstream molecular genetic analyses.