Biostimulants are beneficial microorganisms or substances that can be used in crop production to improve plants' immune responses and their ability to perform well under biotic and abiotic stresses. Biostimulants induce plant resistance to stress factors through systemic acquired resistance or induced systemic resistance. When plants are exposed to virulent and avirulent pathogens, non-pathogenic microorganisms, and some chemicals, the systemic acquired resistance mechanism is activated through the salicylic acid pathway triggering the production of pathogenesis-related proteins. On the other hand, when plants are exposed to beneficial microbes, the induced systemic resistance mechanism is activated through the jasmonic acid and ethylene pathways. The jasmonic acid pathway also leads to pathogenesis-related protein production in plants. In other words, when plants are exposed to pathogens, non-pathogens, or other compounds, various defense genes are activated through two major immune responses, helping plants fight the real infection or prepare them for potential infection. Beneficial microbes and non-microbial biostimulants are like vaccines that prepare plants for potential health problems.