Much of our knowledge on heredity, development, physiology and the underlying cellular and molecular processes is derived from the studies of model, or reference, organisms. Despite the great variety of life, a common base of shared principles could be extracted by studying a few life forms, selected based on their amenability to experimental studies. Very briefly, the origins of a few model organisms are described, including E. coli, yeast, C. elegans, Drosophila, Xenopus, zebrafish, mouse, maize and Arabidopsis. These model organisms were chosen because of their importance and wide use, which made them systems of choice for genome-wide studies. Many of their genomes were between the first to be fully sequenced, opening unprecedented opportunities for large-scale transcriptomics and proteomics studies.