Agriculture is one of the oldest practices in the world to fulfill the food demands of human beings and domestic animals. However, the increasing human population and limited natural resources have emerged as a serious problem to meet the growing food demands. Therefore, novel techniques are continuously being experimented with in agriculture to increase food production and quality. In recent decades, chemical fertilizers and pesticides are largely used to enhance crop productivity. However, it causes serious environmental issues pertaining to soil and water pollution, which adversely affects the ecosystem and living organisms. Recently, the use of nanotechnology in agriculture has proven to be effective in enhancing productivity and reducing the excess use of chemicals. Over the past few years’ adverse effects of chemically synthesized nanoparticles (NPs) on the environment have also been observed. Therefore, researchers are exploring biologically synthesized nanoparticles (Green NPs) for agriculture, therapeutics, and environmental pollution remediation applications. Among these, the use of algae for nanoparticle synthesis, i.e., Phyconanotechnology is emerging as a promising and sustainable alternative to traditional synthesis techniques. With this background, recent advances in phyconanotechnology and their further applications in agriculture for improving crop productivity have been thoroughly discussed in the chapter. The applications of phyconanoparticles (PNPs) as biofertilizers, biopesticides, and other plant growth and yield-promoting activities have been explored.