In the special issue on “Specificity and Variability of Genetic Recombination”, various aspects of genetic recombination in Escherichia coli are tried to understand in terms of biochemistry and biophysics rather than molecular genetics. The papers are grouped into the following four sections: (1) General recombination; (2) Site specific and half site specific recombination; (3) Illegitimate recombination; and (4) In vitro recombination. In the first section, the major role of the recA gene in genetic recombination is discussed and new findings obtained from the analysis of recA transducing phage presented by H. Ogawa. Also multiple pathways of recombination in E. coli are reviewed by S. Shinoura and T. Kato. In the second section, based on their genetic analysis of integration and excision of lambda phage, the structure of the lambda attachment site was discussed by Y. Fukumaki and K. Shimada. The integration mechanism of mu phage was studied by constructing λ-mu hybrid phage and presented by T. Ogawa. A new classification of repeated DNA sequences, including the IS sequences, was introduced and different aspects of episome-host interaction discussed in relation to the interaction between the repeated sequences by H. Ohtsubo and E. Ohtsubo. In the third section, new types of DNA duplications in lambda phage were presented and discussed with respect to the replication error in the origin and termination site by H. Yamagishi and various cases of excision of the λ transducing phage carrying suppressor tRNA genes were introduced by H. Inokuchi and H. Yamagishi. In the fourth section, substrate specificity and variability of restriction enzymes were reviewed by E. Akaboshi and K. Matsubara. Finally, the dynamic aspects of DNA as the substrate for integrative recombination were stressed in the work on DNA gyrase by K. Mizuuchi in collaboration with H. Nash, M. Gellert and R. Weisberg. This issue is headed by the Preface by H. Yamagishi and K. Okamoto (Editors) and the Introduction by H. Ozeki. It is followed by the Epilogue which is a brief survey of recombination models by Y. Ryo. The epilogue introduces the concept of “Recombination of Recombination Models” which in itself becomes an appropriate prologue for future issues.

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