Functional medicine is a dynamic approach to assessing, preventing, and treating complex chronic disease. Functional medicine helps clinicians identify and ameliorate dysfunctions in the physiology and biochemistry of the human body as a primary method of improving patient health. Functional medicine acknowledges that chronic disease is almost always preceded by a lengthy period of declining function in one or more of the body’s systems. Returning patients to health requires reversing (or substantially improving) the specific dysfunctions that have contributed to the disease state. Those dysfunctions are, for each of us, the result of lifelong interactions among our environment, our lifestyle, and our genetic predispositions. Each patient, therefore, represents a unique, complex, and interwoven set of influences onintrinsic functionality that have set the stage for the development of disease or the maintenance of health.