Plastics contribute the most to the ever-growing buildup of pollution in Earth’s water bodies. In the aquatic environment, plastic essentially exists in multiple forms before and following passage to nature depending on its synthetic pathway and succeeding degree of fragmentation or degradation, and includes bulk material, as well as nanosized particles. It is of utmost importance to understand the ecological and biological consequences of nanoparticle release to nature considering that their properties differ considerably from their corresponding bulk material. This chapter highlights recent findings concerning sources, degradation pathways, and ecotoxicity of the nanoparticles derived from plastic degradation in addition to those intentionally fabricated to their form in aquatic systems. (Less)