Analysis of experimental mouse chimeras (chimaeras) and mosaics provides a means of investigating patterning and differentiation within the developing mammalian eye. Chimeric and mosaic mice carry two or more genetically distinct cell populations and extend the repertoire of analytical tools available to the geneticist. Here we review the impact these techniques have had on our understanding of eye organogenesis. Chimeras and mosaics are routinely used to investigate cell lineages, patterns of growth and gene function, and provide a means to clear analytical hurdles that otherwise limit standard genetic approaches. In particular, chimeras are used to investigate the roles of genes in tissues that do not develop in conventional mutant or knock-out mice, to test whether genes act cell autonomously or non-autonomously in different tissues and to dissect tissue-tissue interactions in less tractable, complex systems. Chimeras, in which cells of different genetic composition are mixed at a fine-scale cellular level, may provide qualitatively different data from mosaic mice with conditional knockouts. The uses of chimeras, Cre-loxP mosaics and in vitro tissue recombination for study of ocular organogenesis are compared. Wider use of mosaics and chimeras should provide further insights into eye development.