Phytochemicals are health-protecting compounds of plant origin. They provide flavour and colour to edible fruits, plants, herbs and beverages. Health protecting effects of phytochemicals are due to anti-inflammatory, antioxidant, antiviral, antibacterial, anticarcinogenic, and cellular repair properties. There has been considerable interest in defining biological activities of phytochemicals at the molecular level. The effects of phytochemicals can be conducive, additive, synergistic, and antagonistic. Through these properties, phytochemicals modulate cellular differentiation, proliferation, oxidative stress, inflammation and apoptosis. This book presents an integrated view on molecular mechanisms of beneficial effects of phytochemicals action in acute and chronic humans.