What is addiction?

Today I sought to find a working definition of addiction. I used the aurora library to find some sources to get started. The following links all seem like they may be helpful. And bring up new questions about the causes and conditions of addiction as well as treatment.

http://0-www.annualreviews.org.skyline.ucdenver.edu/doi/full/10.1146/annurev.psych.54.101601.145237
This link has an article that discusses the science behind addiction and offers several models to explain why addicts can't stop.

http://tb4cz3en3e.search.serialssolutions.com/?sid=sersol&SS_jc=TC0000909302&title=Addiction
"Preface to 'What Is Addiction?'." Addiction. Ed. Christina Fisanick. Detroit: Greenhaven Press, 2009. Opposing Viewpoints. Opposing Viewpoints in Context. Web. 12 Mar. 2014.
In this article, the author makes the distinction between soft and hard addictions. "Self-help author Judith Wright refers to non-drug addictions as 'soft addictions'." The author then say, "For years, the concept of addiction included abuse of drugs and alcohol, and only recently have addiction authorities revised the concept. According to Connie Limon of Disabled World, "An addiction of any type is readily recognized by the fact that it is not a matter of choice. Individuals who are addicts do not have the ability to decide to stop abusing'." Another definition is: "the National Institute on Drug Abuse (NIDA) defines addiction as "a chronic, often relapsing brain disease that causes compulsive drug seeking and use despite harmful consequences to the individual who is addicted and to those around them'."

http://tb4cz3en3e.search.serialssolutions.com/?sid=sersol&SS_jc=TC0000909302&title=Addiction
This article provides interesting information about the justice system's impact on treatment.

What I have gathered from these links in regards to my earlier question about what defines addiction is that addiction definitions vary. Some definitions include behavioral addictions such as shopping, sex and gambling. For my research I would like to focus on chemical addictions to alcohol and drugs. The first link I found might be very helpful with learning more about the neurological processes that lead to addiction.