The article presents the main discoveries of Prof. Andrzej K. Tarkowski, which proved to be fundamental for modern mammalian developmental biology and also for progress in animal breeding and assisted reproduction. Among his achievements the most important are: the demonstration of regulative abilities of blastomeres isolated from early mammalian embryos, generation of first chimaeric mice, studies on mammalian parthenogenesis and establishment of blastomere electrofusion technique for production of tetraploid embryos. Studies on nucleocytoplasmic interactions in germ cells and early embryos contributed substantially to the development of mammalian cloning. Prof. Tarkowski’s work and discoveries provided a tremendous input to the contemporary developmental biology of mammals.