The research on the effects of various nanomaterials on seed germination and seedling development has resulted in a vast amount of data, with both positive and negative effects observed depending on the characteristics of the nanoparticles including size, structure, and concentration. This book aims to summarize and highlight the stimulatory and phytotoxic effects of different nanoparticles on seed germination and seedling growth, as well as the characteristic parameters of the nanomaterials responsible for the specific responses. Furthermore, it also includes the reported cellular, molecular, and physiological responses underlying the specific effects.