In order to introduce new desirable characters into the cultivar assortment of lily a range of interspecific crossing barriers has to be overcome. By using various pollination and embryo rescue techniques pre- and postfertilization barriers were overcome and a range of wide interspecific lily hybrids between species and cultivars from the different sections of the genus Lilium could be made. Important breakthroughs include the development of the LA- (L. longiflorum x Asiatic hybrids), the LO- (L. longiflorum x Oriental hybrids) and the OA- (Oriental x Asiatic hybrids) hybrids. In general wide interspecific lily hybrids show F1-sterility. Using somatic chromosome doubling techniques (mitotic polyploidization) tetraploids with restored fertility can be produced from these diploid hybrids. An alternative method is the use of unreduced (or 2n) gametes (meiotic polyploidization), which are rarely found in some hybrids. Introgression of alien chromosome segments from donor species into recipient cultivar through backcrossing of F1 hybrid was studied using in situ hybridization techniques (GISH). Mitotic polyploidization showed no homoeologous recombinations between the parental genomes whereas meiotic polyploidization detected many. The use of 2n-gametes seems to be the most promising way for the introgression of desirable characters.