Plants have developed diverse defense mechanisms to protect against pests, with secondary metabolites playing a critical role. These organic compounds, not directly involved in primary metabolism, act as natural pesticides, toxins, or deterrents, reducing herbivory and pathogen invasion. Secondary metabolites include alkaloids, phenolics, terpenoids, and glucosinolates, each contributing uniquely to plant defense. For instance, alkaloids disrupt herbivore nervous systems, phenolics deter feeding, terpenoids serve as toxins and attract beneficial predators, while glucosinolates release toxic compounds upon tissue damage. These defenses are part of an evolutionary arms race between plants and herbivores, driving adaptations on both sides. As concerns over synthetic pesticides grow, secondary metabolites offer promising avenues for sustainable pest management in agriculture.