Buprenorphine can be used for the treatment of opioid addiction or for the treatment of chronic pain.
Suboxone is the sublingual form of buprenorphine most commonly used for the treatment of addiction.  In order for a physician to prescribe Suboxone for addiction, they must have obtained a special DEA waiver to do so.  Currently, only physicians can obtain this waiver.  Physicians who have been prescribing for less than a year are limited to 30 patients at any given time on Suboxone.  Those physicians who have been prescribing for more than a year can apply for an addictional DEA waiver to increase their treatment to 100 patients.
Buprenex is an injectable form of buprenorphine which is FDA approved for the treatment of moderate to severe pain.  0.3mg of Buprenex are equivalent to 10mg of injectable morphine.  Buprenex is not FDA approved for the treatment of addiction.
Many physicians who treat chronic pain, are now prescribing Suboxone for the treatment of chronic pain in individuals who have a history of opioid addiction.  This is an "off label" use of the medication.  Any provider with a schedule III DEA license can prescribe Suboxone for this purspose.  Most providers who are using Suboxone in this way strive to ensure that the individuals addiction is in remission as a contingency to precribing buprenorphine.
Suboxone also contains Naloxone, which is an opioid antagonist (blocker).  When discolved under the tongue, only tiny amounts of Naloxone are absorbed.  If a Suboxone tablet is injected, all of the Naloxone is absorbed and the individual experiences precipitated withdrawal as a consequence.  The presence of Naloxone thus acts as a safety feature to prevent individuals from injecting Suboxone.
Subutex, is a sublingual (under the tongue) form of pure buprenorphine.  It is not commonly precribed in the US due to the potential for abuse by injection.
Precipitated withdrawal can also occur if one uses buprenorphine too soon after taking other opioids.  Individuals starting buprenorphine must undergo a "buprenorphine induction" to avoid experiencing precipitated withdrawal.

AFM Article Buprenorphine Tx 07.pdf111.95 KB
AFP Buprenorphine Tx 5.05.pdf185.56 KB
NEJM Bup 9.03.pdf107.03 KB
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AJT: Buprenorphine for Pain 2005.pdf76.77 KB
methadone to morphine to bup 2006.pdf126.83 KB