The last few years have seen an absolute explosion of results on the early regional specification of the fruit fly Drosophila melanogaster, and the work is now so advanced that we are approaching a satisfactory explanation of the developmental program itself. This has been achieved by a brilliant combination of developmental genetics, experimental embryology and molecular biology. Because of the small size of Drosophila and its short life cycle of two weeks, it has been intensively used in genetic research for most of the present century and over this time a large number of mutants have been collected and accurate genetic and cytological maps of the chromosomes have been compiled. Over most of this period the developmental genetics dealt only with mutants which were viable as adults but from the late 1970s it was realized that many mutations of the genes controlling regional specification would lead to grossly perturbed body plans and be lethal by late embryonic life. The raw material for the breakthrough was a near comprehensive collection of late embryo lethal mutations affecting the body plan which were isolated in massive screens mainly by Ch. Nüsslein-Volhard, E. Wieschaus, T. Schüpbach and colleagues. Another crucial element of the breakthrough was the tradition of insect experimental embryology, mainly a German subject, which had previously been conducted on insect species other than Drosophila.