In the wake of the numerous now-fruitful genome projects, we are nng an era rich in biological data. The field of bioinformatics is poised to oit this information in increasingly powerful ways; but the abundance and ngcomplexity both of the data and the tools and resources required to analyze them are threatening to overwhelm us. Databases and their search tools are now an essential part of the research environment, However; the rate of sequence generation and haphazard proliferation of databases have made it difficult to keep pace with developments. In an age of information overload, researchers want rapid, easy to use, reliable tools for functional characterization of newly determined sequences. But what are those tools? How do we access them? Which should we use? This review focuses on a particular type of database that is increasingly used in the task of routine sequence analysis the so-called pattern database. The paper aims to provide an overview of the current status of pattern databases in common use, outlining the methods behind them and giving pointers on their diagnostic strengths and weakness.