Nanotechnology is a widely used tool in various fields of everyday life, such as industry, medicine, and agriculture. In addition, nanomaterials (NMs) have been shown to be useful for fertilizer, pesticide, and biostimulant applications. Plant biostimulation is an area of agricultural science in which there has been widespread interest in the multiple advantages of cultivable species, such as increased productivity, resistance to biotic and abiotic stress, and more efficient use of water and minerals. Several studies have shown that different NMs can potentially be applied as plant biostimulants, resulting in positive responses in crops. Among these responses are modifications in gene expression in plant cells, which positively or negatively alter certain proteins involved in the different metabolic processes of plants. On the other hand, the application of NMs also alters the enzymatic activity of a wide variety of plant enzymes. Changes in both the structure and production of proteins, as well as in enzymatic activity, will result in greater or lesser efficiency in physiological processes such as photosynthesis, respiration, and assimilation of nutrients, among others. Therefore, the aim of this chapter was to review in detail how different NMs induce biostimulation in plant species, in addition to their effects on proteins and enzymatic activity, emphasizing the physiological processes mentioned above.