Criminal defense lawyers have several legal strategies at their disposal, including a claim of police or governmental entrapment. Legally speaking, entrapment occurs whenever a police officer or other government agent deceives an innocent person into committing a crime he or she had no prior intention of committing. If a court determines that the charges against the defendant are based on entrapment, he or she cannot be convicted of the crime. The laws against police or governmental entrapment are intended to prevent law enforcement agencies from coercing a citizen into committing a crime, then arresting him or her for the act.

Entrapment charges often stem from vice crimes involving drugs, gambling or prostitution. Law enforcement agencies have the legal right to present their officers as drug dealers, prostitutes, gambling bookmakers or other professional criminals. Contrary to popular belief, these undercover agents do not have to reveal their true identities or legal affiliation when asked. It is not considered police entrapment if an undercover officer presents a supply of drugs to a potential buyer, for example. The buyer of those drugs commits a crime once the deal has been made, not during the initial contact with the undercover officer.

Law enforcement officers must be aware of their limitations during a sting operation to avoid later accusations of entrapment. An undercover officer working as a prostitute, for example, cannot initiate a conversation leading to the customer's solicitation offer. A defendant arrested for solicitation of a prostitute could claim that the undercover officer was flirtatious or made physical contact before identifying herself as a prostitute. An argument could be made that the solicitation was based on the officer's behavior, not on the defendant's intention to commit a crime.

Claims of entrapment can be notoriously difficult to prove. Some successful claims against law enforcement agencies have centered around the idea of a 'virtue test'. Police cannot select random citizens to participate in organized sting operations in hopes of generating an arrest. There must be some compelling evidence that a specific individual has a propensity for committing such a crime.

Another reason entrapment is difficult to prove in court is the criminal history of the defendant. If the prosecution can demonstrate a previous history of similar crimes, then it becomes extremely difficult to prove entrapment. Providing an opportunity to commit a crime is not considered entrapment.

This is why police stings involving Internet sex crimes have been successful. Defendants may claim that adult police officers posing as underage chatroom participants constitutes entrapment, for instance. The reality is that the undercover agent only provided an opportunity for the suspect to initiate illegal conversations.

There have been a number of successful entrapment defenses mounted throughout the years, mostly involving high-level government stings. The operation itself may become criminal in nature, or an overzealous agent may use coercive techniques to pressure someone into committing a crime. Many cases involving possible entrapment become very high-profile, such as the drug case against former automaker John DeLorean during the 1980s or the Abscam case involving a number of federal lawmakers accused of accepting bribes from foreign investors.