Turmeric (the rhizome of Curcuma longa Linn.) has been used as a spice, food flavoring and coloring agent, and in medicinal preparations for various diseases including cough, diabetic wounds, hepatic and cardiovascular disorders in Eastern civilization for a long time. Curcuminoids and essential oil are the major components of turmeric, which have shown various bioactivities and promising results in various research investigations. Particularly, curcumin has demonstrated powerful efficacy as an anticancer agent, which possesses antiinflammatory, antioxidant, anti-Alzheimer, and anticancer activities in both preclinical and clinical studies. Moreover, curcumin has hepatoprotective, neuroprotective, cardioprotective, hypoglycemic, antirheumatic, and antidiabetic activities. Recently research indicated that the ar-turmerone, α-turmerone, and β-turmerone were the biologically active constituents in the essential oil, and proved their antimicrobial, antioxidative, antiinflammatory activity, and anticancer potentials. Turmeric oil is also widely used in pharmaceutical and cosmetic applications. Therefore, both curcuminoids and volatile components are the basis for healthy efficiencies of turmeric. This chapter will summarize the chemical composition and quality control methods of turmeric, the recent biological studies of curcuminoids and turmeric oil. The pharmaceutics studies and application are also summarized.