For the plant breeder, one of the objectives of cell culture systems should be their exploitation for the induction and isolation of mutant cells, which can then be regenerated as mutant plants. While a number of mutations have been recognized in plant cells in vitro, few have had any significance for plant breeding. There are currently a number of constraints to the exploitation of this technology, some of which are related to methodological limitations; these are likely to be overcome, but others, which relate to the nature of the attributes that the plant breeder seeks to modify, are much more intractable. There is scope for exploiting cell cutures as genetic tools, as has already been done with animal cell cultures. In contrast, the culture of organized tissues in the form of meristems or small shoots has begun to be useful a technique for plant breeders, and examples of diverse applications will be discussed. Most exploit the rapid rates of multiplication, and the assured health status of the propagules, that can be attained in culture; there is also the possibility of manipulating the genotype of these tissues. Finally, organ culture, and it is the culture of embryos that is of mostinterest to the plant breeder in this context, is considered; the value of embryo culture as a means of producing novel interspecific and intergeneric hybrids is well recognized. In addition, cultured embryos can be used as experimental systems for studying the biochemistry and molecular biology of storage product synthesis and accumulation.