In the past few years, novel techniques have loomed that permit the employment of plants as manufacturing factories to transiently and frequently express targeted genes of interest with high efficiency, either endogenous or exogenous, in their endemic or modified form. The aforestated strategies permit and expedite targeted gene products for both research and commercial objectives, mitigating the requirement of extensive, tedious, and burdensome stable plant transformation. Moreover, transient expression studies also circumvent the regulatory constraints that are associated with these transformations. Co-expression of proteins for the production of macromolecules and analysis of metabolic pathways can also be effectively achieved using transient expression systems. Three expression systems are employed for transient delivery in plants: biolistic bombardment of leaves with nucleic acids encoding the gene of interest, Agrobacterium-mediated transformation of T-DNA fragments, and plant viral vectors. Plant viruses proliferate independently, increasing the possibility of infecting plants in the ecosystem. Needle-less syringes, high-pressure sprays, and vacuum infiltration methods are used to deliver Agrobacterium suspension into plant leaves, where the gene of interest is transferred into the nucleus of host plants via T-DNA delivery.