The recent achievements in engineering studies on plant cell cultures are reviewed, included are the gas concentration effects and bioprocess integration for the enhanced productivity of plant secondary metabolites. The metabolic engineering of plant secondary metabolite pathways and recombinant protein production from genetically modified plant cells are introduced. Large-scale plant micropropagation via somatic embryogenesis and hairy roots is discussed for efficient propagation of desease-free, genetically uniform and massive amounts of plants in vitro in massive amounts. Characterization and application of hairy plant roots endowed with photosynthetic functions is also covered in this special volume.