Genomics is the discipline that has grown up around the sequencing and analysis of complete genomes. It has typically emphasized questions that involve the biological function of individual organisms, and has been somewhat isolated from the fields of evolutionary biology and ecology. However, genomic approaches also provide powerful tools for studying populations, interactions among organisms, and evolutionary history. Because of the large number of microbial genomes available, the first widespread use of genomic methods in evolution and ecology was in the study of bacteria and archaea, but similar approaches are being applied to eukaryotes. Genomic approaches have revolutionized the study of in situ microbial populations and facilitated the reconstruction of early events in the evolution of photosynthetic eukaryotes. Fields that have been largely unaffected by genomics will feel its influence in the near future, and greater interaction will benefit all of these historically distinct fields of study.