This study presents a genomic analysis of two uncultured marine viral communities. Over 65% of the sequences were not similar to previously reported sequences, indicating much of the diversity is uncharacterized. The most common hits were to viruses, including sequences from major dsDNA tailed phage families and some algal viruses. Mathematical models suggested the most abundant viral genome comprised 2–3% of the total population, with 374–7,114 viral types. The diversity of the viral communities was extremely high, and it was possible to sequence the entire genome of an uncultured marine viral community. Marine viruses, mostly phages, have significant impacts on global biogeochemical cycles, microbial diversity, and genetic exchange. However, little is known about marine viral biodiversity or the evolutionary relationships of marine and nonmarine viruses. Viruses are difficult to culture, and they lack conserved genetic elements for diversity and evolutionary distance markers. To overcome these limitations, the researchers developed a method to shotgun clone and sequence uncultured aquatic viral communities. The study isolated viral community DNA from surface seawater samples using differential filtration and density-dependent gradient centrifugation. The viral DNA was then randomly sheared, end-repaired, and amplified to create a shotgun library. Sequencing of the libraries revealed that most sequences had no significant hits to previously reported sequences, suggesting much of the diversity is uncharacterized. The majority of the virus hits were similar to phages, and significant hits to phages were classified into phage families. The researchers used mathematical models to estimate the number of viral types in the communities. The power-law model predicted 3,318 viral types in the SP community and 7,114 in the MB community. The diversity of these communities was extremely high, with Shannon Indices of 7.56 and 7.99, respectively. The results suggest that it is possible to sequence the entire genome of an uncultured marine viral community. The study highlights the importance of marine viruses in global biogeochemical cycles and their potential role in microbial diversity and genetic exchange. The findings also emphasize the need for further research into marine viral biodiversity and the evolutionary relationships of marine and nonmarine viruses.This study presents a genomic analysis of two uncultured marine viral communities. Over 65% of the sequences were not similar to previously reported sequences, indicating much of the diversity is uncharacterized. The most common hits were to viruses, including sequences from major dsDNA tailed phage families and some algal viruses. Mathematical models suggested the most abundant viral genome comprised 2–3% of the total population, with 374–7,114 viral types. The diversity of the viral communities was extremely high, and it was possible to sequence the entire genome of an uncultured marine viral community. Marine viruses, mostly phages, have significant impacts on global biogeochemical cycles, microbial diversity, and genetic exchange. However, little is known about marine viral biodiversity or the evolutionary relationships of marine and nonmarine viruses. Viruses are difficult to culture, and they lack conserved genetic elements for diversity and evolutionary distance markers. To overcome these limitations, the researchers developed a method to shotgun clone and sequence uncultured aquatic viral communities. The study isolated viral community DNA from surface seawater samples using differential filtration and density-dependent gradient centrifugation. The viral DNA was then randomly sheared, end-repaired, and amplified to create a shotgun library. Sequencing of the libraries revealed that most sequences had no significant hits to previously reported sequences, suggesting much of the diversity is uncharacterized. The majority of the virus hits were similar to phages, and significant hits to phages were classified into phage families. The researchers used mathematical models to estimate the number of viral types in the communities. The power-law model predicted 3,318 viral types in the SP community and 7,114 in the MB community. The diversity of these communities was extremely high, with Shannon Indices of 7.56 and 7.99, respectively. The results suggest that it is possible to sequence the entire genome of an uncultured marine viral community. The study highlights the importance of marine viruses in global biogeochemical cycles and their potential role in microbial diversity and genetic exchange. The findings also emphasize the need for further research into marine viral biodiversity and the evolutionary relationships of marine and nonmarine viruses.