Publisher Summary This chapter provides a comprehensive review of the current state of knowledge in using in vitro plant cultures for producing macromolecules (with an emphasis on using cultured plant cells) and small molecules (with an emphasis on using hairy roots). It focuses on the latest advances in applied cell physiology and process techniques pertinent to large-scale industrial bioprocess development. In addition, technological innovations are proposed for the improved utilization of renewable resources in industrial plant cell culture processes. The chapter is organized into two sections, one focuses on high molecular weight products (mainly recombinant proteins), and the other on low molecular weight products (mainly secondary metabolites). An important benefit of using plant tissue cultures for recombinant protein production is their capability to perform the complex post-translational modifications necessary for active biological functions of the expressed heterologous proteins. Plant cell culture processes for protein production encompass upstream and downstream processing similar to conventional recombinant fermentation processes. Molecular strategies are being used to improve heterologous protein accumulation in plants and plant cells at the transcription, translation, and post-translation levels.