E.B. Kopp and S. Ghosh, NF-kB and Rel Proteins in Innate Immunity. D.T. Weaver, V(D)J Recombination and Double-Strand Break Repair. P. Kisielow and H. von Boehmer, Development and Selection of T Cells: Facts and Puzzles. G. Kroemer, The Pharmacology of T Cell Apoptosis. G.-K. Sim, Intraepithelial Lymphocytes and the Immune System. B.A. Imhof and D. Dunon, Leukocyte Migration and Adhesion. G. Dranoff and R.C. Mulligan, Gene Transfer as Cancer Therapy. Subject Index. Contents of Recent Volumes.