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.^{: 669–671} 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 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 defence, 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 recognised by common law until the case of b. Rex v. Scofield in 1784.^: 669

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).