1 Introductory remarks.- 2 The enzymology of in vitro DNA recombination.- 3 Plasmid vectors.- 4 Bacteriophage ? vectors.- 5 Expression of cloned DNAs in E. coli.- 6 Methods for the physical characterisation of cloned segments of chromosomal DNA from higher eukaryotes.- 7 Approaches for studying expression in eukaryotic systems.