In the past few years a considerable number of mutagenesis methods and high-throughput screening (HTS) systems have been developed and improved. In parallel, computer programs or software packages for molecular modeling have been further investigated. Thus, the number of examples for successful directed evolution and rational design is increasing constantly. In this review the essential mutagenesis methods and HTS systems, especially for esterases, are described and various examples for the application of these protein engineering tools are provided.