Recently, much evidence has shown that phytochemicals are essential for daily health maintenance just like essential amino acids, vitamins, and minerals. However, some of these components are not able to produce within our bodies. Therefore, we must intake these phytochemicals from external sources. Based on the above fact, this book mainly describes the phytochemicals and their effects, including preventions and treatments as follows: Chapter One: Medicinal Phytochemicals and Health Effects of Henbit Lamium amplexicaule L. Based on Their Evidences; Chapter Two: Natural Carotenoids: Occurrence, Structure, Synthesis and Their Dietary Absorption; Chapter Three: The Phytochemicals and Health Benefits of Murraya koenigii; Chapter Four: Bioactive Compounds from Lippia citriodora: Application in Diseases Prevention; and Chapter Five: Food for Mental Cognition and Brain Health. These chapters will provide more advanced information to researches in the academic region of advanced novel drug designs using phytochemicals.