This review discusses the chemistry and biochemistry of dietary polyphenols, focusing on their classification, extraction, separation, occurrence, biosynthesis, and biological activities. Polyphenols are a diverse group of phytochemicals found in plant-based foods, with over 8000 known structures, including flavonoids, phenolic acids, and other compounds. They play important roles in human health, particularly in preventing chronic diseases such as cancer, cardiovascular disease, and neurodegenerative disorders. Polyphenols act as antioxidants, neutralizing free radicals and modulating cell signaling pathways. They are also involved in the regulation of metal ions and the activation of antioxidant enzymes. The review highlights the importance of understanding polyphenol biosynthesis, which is linked to primary metabolism through intermediates derived from plastids and mitochondria. Separation and identification of polyphenols remain challenging due to their structural diversity and complex glycosylation patterns. Advanced analytical techniques such as HPLC and LC-MS are used for their quantification and identification. The review also discusses the antioxidant activities of polyphenols, including their ability to scavenge radicals and inhibit oxidative stress. Beyond antioxidant functions, polyphenols may also influence cell signaling pathways and have potential applications in disease prevention and treatment. The review emphasizes the need for further research to fully understand the biological roles and health implications of polyphenols.This review discusses the chemistry and biochemistry of dietary polyphenols, focusing on their classification, extraction, separation, occurrence, biosynthesis, and biological activities. Polyphenols are a diverse group of phytochemicals found in plant-based foods, with over 8000 known structures, including flavonoids, phenolic acids, and other compounds. They play important roles in human health, particularly in preventing chronic diseases such as cancer, cardiovascular disease, and neurodegenerative disorders. Polyphenols act as antioxidants, neutralizing free radicals and modulating cell signaling pathways. They are also involved in the regulation of metal ions and the activation of antioxidant enzymes. The review highlights the importance of understanding polyphenol biosynthesis, which is linked to primary metabolism through intermediates derived from plastids and mitochondria. Separation and identification of polyphenols remain challenging due to their structural diversity and complex glycosylation patterns. Advanced analytical techniques such as HPLC and LC-MS are used for their quantification and identification. The review also discusses the antioxidant activities of polyphenols, including their ability to scavenge radicals and inhibit oxidative stress. Beyond antioxidant functions, polyphenols may also influence cell signaling pathways and have potential applications in disease prevention and treatment. The review emphasizes the need for further research to fully understand the biological roles and health implications of polyphenols.