The second edition of Gene Knockout Protocols brings together distinguished contributors with extensive experience in the gene targeting andmouse genetics fields. The new edition particularly emphasizes the range of new mutagenesis techniques developed over the last seven years, but also covers the basic methods relevant to researchers performing classical gene targeting experiments. The 25 chapters of this volume are organized into four sections on gene modification in ES cells, stem cell manipulation, the generation of genetically engineered mice, and mutant phenotype analysis. The contents reflect the diversification of mutagenesis approaches that now include, besides classical gene targeting, gene modification by oligonucleotides, gene trap mutagenesis, RNAi-mediated knockdown, transposon, and ENU mutagenesis.