Complete genome sequences have now been determined for numerous organisms, and many additional projects are under way. These studies are producing tremendous quantities of sequence data. Cataloging, storing, retrieving, and analyzing this huge data set are major challenges of modern genetics. Bioinformatics is an interdisciplinary field that combines molecular biology and computer science. It centers on developing databases, computer-search algorithms, gene-prediction software, and other analytical tools that are used to make sense of DNA-, RNA-, and protein-sequence data. Bioinformatics develops and applies these tools to “mine the data,” extracting the useful information from sequencing projects. The development and use of algorithms and computer software for analyzing DNA-, RNA-, and protein-sequence data have helped to make molecular biology a more quantitative field. Sequence data in publicly available online databases enable scientists and students throughout the world to access this tremendous resource.