This chapter delves into the intricate realm of nanoparticle (NP) phytotoxicity, exploring interactions between engineered nanoparticles and plant systems. We examine the mechanisms governing NP entry, uptake, and translocation within plant tissues, highlighting the influence of NP physicochemical properties on plant physiological processes. Furthermore, we explore NP-induced biophysical and molecular alterations in plants, including free radical damage, cellular damage, and disruptions in nutrient uptake and photosynthesis. We also discuss the ecotoxicological implications of NP phytotoxicity on plant growth, development, and ecosystemic functions.