This book collects some recent scientific data on the role of polyphenols in various pathological contexts, ranging from viral infection to metabolic or chronic disorders such as diabetes and renal fibrosis. The included studies showed both in vitro and in vivo evidence concerning positive effects of polyphenols in inflammation, apoptosis, and oxidative stress. The investigated molecules include: verbascoside from Olea europea, curcumin from Curcuma longa, phenolic acids from Antirhea borbonica, and phlorotannins from marine algae. Finally, the main flavonoids present in the human diet and their anti-inflammatory and anti-cancer roles were also discussed. The scientific data confirm the importance of the plant kingdom, both marine and terrestrial, in the search for new compounds with potential benefits for humans.