Many products of interest are synthesized in organized tissues, but not formed in suspension or callus culture. Therefore, most attention has been focused on root cultures. The transgenic plant,"hairy root", has brought us to dramatic improvements in growth rate and high content of desirable products. Since the roots are quite different from callus in morphology, the culture manner should be explored independently. By providing a growth environment, an elite hairy root can be a more attractive plant. Both of strain selection to generate more competent plants in breeding and engineering development are necessary to overcome various limitations. In this chapter the engineering issues involved in using hairy root culture are discussed, as follows. 1. Measurement of cell concentration on line, and a designing bioreactors for hairy root in liquid culture. 2. High cell density culture and its kinetic parameters. 3. Secretion of target products. 4. The micropropagation of the regenerated hairy root by means of artificial seed system. In some cases where callus and suspension culture show negligible productivity, organ culture will be necessary to achieve good formation. This study on hairy root culture indicates one of the best attempts to the recovery of products from the organ culture in plant biotechnology.