Flavonoids are part of a major group of compounds known as secondary metabolites. In spite of being originally considered as products from plant metabolism without function, they have drawn attention during the last years. These compounds are widely spread throughout higher and lower plants and their applications are becoming more clear after thorough research done on secondary metabolism. Flavonoids added as antioxidants to dietary supplements are generally known as bioflavonoids and are first example of the beneficial effects of flavonoids. Here we summarize different aspects on the role of flavonoids in plant metabolism as well as their interaction with photosynthetic enzymes according to the results obtained in our laboratory.