Plant secondary metabolism plays a relevant role in protecting plants against abiotic-biotic stress. Secondary metabolites are not part of vital plant processes but allow them to survive during harsh environmental conditions. Examples of biotic stress include viruses, bacteria, fungi, and miRNA. Abiotic stress includes low and high temperatures, drought, soil salinity, low and high light intensities, electromagnetic radiation, motion disturbances, acoustic emissions, nutrient deficiency, nanoparticles, and heavy metals. In this sense, when applied at low doses to plants, those stress factors can induce positive effects and become eustress. However, if irreversible damage is generated, the result is called distress. Research on each type of stress has been performed in plants to enhance yield and increase the production of secondary metabolites of commercial interest or to confer plants with better nutraceutical value. This chapter describes the role of abiotic-biotic stress in plant secondary metabolites production, their classification, and the hormetic curve.