Molecular farming is a biotechnological approach that includes the genetic adjustment of agricultural products to create proteins and chemicals for profitable and pharmaceutical purposes. Plant molecular farming describes the manufacture of recombinant proteins and other biologically active product in plants. This approach depends on a genetic transformation of plants that can be accomplished by the methods of stable gene transfer, such as gene transfer to nuclei and chloroplasts, and unstable transfer methods like viral vectors. The requirement for recombinant proteins in terms of quality, quantity, and diversity is increasing exponentially This demand is traditionally met by recombinant protein construction technologies and the engineering of orthodox expression systems based on bacteria or mammalian cell cultures. However, majority of developing countries cannot afford the high costs of medicine derived from such existing methods. Hence, we need to produce not only the new drugs but also the cheaper versions of those already present in the market. Plant molecular farming is considered as a cost-effective technology that has grown and advanced tremendously over the past two decades. This book summarizes the advances and challenges of plant molecular farming for all those who are working on or have an interest in this rapidly emerging area of research.