Addiction is a chronic disorder proposed to be precipitated by a combination of genetic, biological/pharmacological and social factors.
Addiction is now narrowly defined as "uncontrolled, compulsive use"; if there is no harm being suffered by, or damage done to, the patient or another party, then clinically it may be considered compulsive, but to the definition of some it is not categorized as "addiction".
Addictions can theoretically form for any rewarding behavior, or as a habitual means to avoid undesired activity, but typically they only do so to a clinical level in individuals who have emotional, social, or psychological dysfunctions, taking the place of normal positive stimuli not otherwise attained (see Rat Park).
Addiction is an uncontrollable compulsion to repeat a behavior regardless of its negative consequences.
While addiction or dependency is related to seemingly uncontrollable urges, and may have roots in genetic predisposition, treatment of dependency is always classified as behavioral medicine.
It is frequently noted that certain addictions "run in the family," and while researchers continue to explore the extent of genetic influence, there is strong evidence that genetic predisposition is often a factor in dependency.