In vitro plant cell cultures have provided a tool for studying plant metabolism and physiology and to explore productive processes of secondary metabolites. More recently, genetic engineering has allowed the use of in vitro cultures to modulate plant biosynthetic pathways and to express heterologous proteins of biomedical relevance. The aim of this book is to offer background information to students and researchers in the fields of Plant Biotechnology and Molecular Farming about the potential of in vitro cultures to perform phytofermentations and molecular farming. Also, the application of in vitro cultures for the production of specific secondary metabolites and recombinant proteins is reviewed.