The increasing knowledge on the health benefits of certain food ingredients, in particular, those of plant origin, opened the discussion of the possibility of using edible plants or their active components in the prevention of non-communicable diseases. The health-promoting properties of plant foods are related to the presence of non-nutritive compounds, mainly plant secondary metabolites, which can affect many biological mechanisms critical for the proper functioning of the human body. This chapter presents an overview of the most commonly consumed secondary metabolites found in the food, including phenolics, terpenoids, nitrogen/sulfur-containing compounds such as betalains, purine alkaloids, glucosinolates, and sulfoxides, along with their classification, examples, sources, processing effect, and health benefits. © 2023 selection and editorial matter, Hanna Staroszczyk and Zdzislaw E. Sikorski; individual chapters, the contributors.