About SVUWarning: Contains spoilers for seasons 5+ Law & Order: Special Victims Unit (also known as Law & Order: SVU or simply SVU) is a part of the Law & Order franchise. It is not technically a spin-off, as the format of the show differs in many ways from the original Law & Order. Law & Order focuses half the show on the police investigating the crimes and the other half on the ADAs prosecuting the offenders. Special Victims Unit largely focuses on the police and has courtroom scenes for only a small part. In some episodes, the courtroom doesn't feature at all. The characters' lives also play a part in SVU, whereas in the original Law & Order, they are hardly ever mentioned. The show was originally going to be called Sex Crimes, but it was believed that this sounded much too harsh and so it was decided to put it under the Law & Order franchise. The theme tune is the same as that for Law & Order, but it is remixed. At the start of each episode, the following is said:
In the criminal justice system, sexually based offences are considered especially heinous. In New York City, the dedicated detectives who investigate these vicious felonies are members of an elite squad known as the Special Victims Unit. These are their stories.The show focuses on crimes such as rape, sexual assault and paedophilia and also those involving children and the elderly. At the forefront of the show are Detectives Elliot Stabler and Olivia Benson. Stabler has five children and enjoyed life as a family man until his wife left him and took the children after many years of marriage (season six). As a result, he became increasingly unstable, his anger issues becoming more apparent. His wife returned to him in season eight. Benson is a child of rape and this is what made her want to join the squad. Her mother raised her alone and was a chronic alcoholic (presumably because of what happened to her). She died falling down some steps when drunk (season two). Both Stabler and Benson are very competent cops and extremely dedicated to their work.
The other two main detectives in the squad are John Munch and Odafin "Fin" Tutuola. Munch is a very competent cop, but known to be a little paranoid, often talking about conspiracy theories and is very sarcastic. He transferred from Baltimore (Homocide: Life On The Street) to join the squad. Tutuola is street smart and tough, but still shows compassion. He worked in narcotics before joining the squad (in season two).
The detectives are led by Captain Don Cragen. Cragen had a problem with alcohol in his past, but has been sober for a number of years. (His character previously appeared in Law & Order). The other two main characters are ADA Casey Novak and Doctor George Huang. Novak started working with the squad (season five) after ADA Alex Cabot was shot. After the first case, she wasn't sure if she could handle it, but DA Branch and Detective Benson convinced her to stay. She is sensitive to cases involving issues of psychiatric illness, as her fiancé from college developed schizophrenia and he refused treatment. Dr. Huang is a profiler and offers valuable insight to the detectives, helping them to identify suspects. He also helps the detectives with interrogation tactics and sometimes gets involved directly. Previous characters include ADA Alexandra "Alex" Cabot and Detectives Brian Cassidy and Monique Jeffries. Cabot left because of a case connected to a Colombian drug cartel (episode 5.04 "Loss"). She was put into witness protection after she was shot and nearly killed in a drive-by shooting. The FBI fixed it so that everybody believed she was dead. The only two to know that she was in witness protection were Detectives Benson and Stabler, until she made an appearance after the person responsible for her shooting was caught and she was brought in to testify (episode 6.16 "Ghost"). Unfortunately, the shooter's connections made it necessary for Cabot to be kept in witness protection.
Cassidy was new to the squad, but left after only a few cases because he couldn't handle it. The cases really got to him and Captain Cragen organised for him to be transferred to narcotics (episode 1.13 "Disrobed"). Jeffries was dismissed from the squad after a compulsory psych evaluation of all the squad detectives found her to be "on the edge" (episode 2.01 "Wrong Is Right"). There are also several recurring characters. See the character list here. If you'd like to know about the basis of the show or the impact that it has had, read this.