An attempt to commit a crime occurs if a criminal has an intent to commit a crime and takes a substantial step toward completing the crime, but for reasons not intended by the criminal, the final resulting crime does not occur. Attempt to commit a particular crime is a crime, usually considered to be of the same or lesser gravity as the particular crime attempted. Attempt is a type of inchoate crime, a crime that is not fully developed. The crime of attempt has two elements, intent and some conduct toward completion of the crime.

One group of theories in criminal law is that an attempt to commit an act occurs when a person comes dangerously close to carrying out a criminal act, and intends to commit the act, but does not commit it. The person may have carried out all the necessary steps (or thought they had) but still failed, or the attempt may have been abandoned or prevented at a late stage. The attempt must have gone beyond mere planning or preparation, and is distinct from other inchoate offenses such as conspiracy to commit a crime or solicitation of a crime. There are many specific crimes of attempt, such as attempted murder, which may vary by jurisdiction. Punishment is often less severe than would be the case if the attempted crime had been carried out. Abandonment of the attempt may constitute a not guilty defense, depending partly on the extent to which the attempt was abandoned freely and voluntarily. Early common law did not punish attempts; the law of attempt was not recognized by common law until the case of b. Rex v Scofield in 1784.

The essence of the crime of attempt in legal terms is that the defendant has failed to commit the actus reus (the Latin term for the "guilty act") of the full offense, but has the direct and specific intent to commit that full offense. The normal rule for establishing criminal liability is to prove an actus reus accompanied by a mens rea ("guilty mind") at the relevant time (see concurrence and strict liability offenses as the exception to the rule).

The actus reus (guilty act) of attempted crime.

Whether the actus reus of an attempt has occurred is a question of fact for the jury to decide after having heard the judge's instructions regarding the law. The common law precedent is used to distinguish between acts that were merely preparatory and those sufficiently proximate or connected to the crime. However, sometimes it is hard to draw the line between those acts which were merely preparatory, and those that went and executed a plan, will always go through a series of steps to arrive at the intended conclusion. Some aspects of the execution of the act will be too remote or removed from the full offense. Examples are watching the intended victim over a period of time to establish the routines and traveling to a store to buy necessary tools and equipment. But the closer to the reality of committing the offense the potential wrongdoer moves, the greater the social danger they become. This is a critical issue for the police who need to know when they can intervene to avert the threatened harm by arresting the person. This is a difficult policy area. On the one hand, the state wishes to be able to protect its citizens from harm. This requires an arrest at the earliest possible time. But, most states recognize a principle of individual liberty that only those people who actually choose to break the law should be arrested. Since the potential wrongdoer could change their mind at any point before the crime is committed, the state should wait until the last possible minute to ensure that the intention is going to be realized.