This volume contains a selection of articles from volumes 216, 217 and 218 of "Methods in Enzymology". Key features include methods for: DNA isolation and cloning; synthesizing complementary DNA (cDNA); cleaving and manipulating DNA; selecting useful reporter genes; constructing vectors for cloning genes; constructing expression vectors; site-directed mutagenesis and gene disruption; identifying and mapping genes; transforming animal and plant cells; sequencing DNA; amplifying and manipulating DNA by PCR; and detecting DNA-protein interaction.