Phytoplasmas are pleomorphic, non-culturable, wall-less prokaryotes that colonize phloem tissues of several plant species inflicting yellows-type diseases. They are transmitted between plants by vegetative propagation, and insect vectors are the chief means of dissemination of phytoplasmas. This chapter summarizes recent progress in phytoplasma research, focusing on molecular division, phytoplasma–insect vector interactions, molecular mechanisms of insect transmissibility, vector dispersal, serological and molecular diagnostic tools for detection and characterization of phytoplasma, practices for sustainable disease management, and important phytoplasma diseases in India.