Abstract: Punishment of criminal attempts increases deterrence: both attempts that result & those that do not result in harm have to be sanctioned in order to demonstrate that the expected sanction exceeds the benefit (presented as a probability-discounted model of expected sanction). If full information on the criminal act is available to the courts, then the potential harm is calculated, & the imposed sanction can be equal to the sanction for causing harm. If the knowledge about the act is imperfect, the court should follow the same basic procedure, & obtain information about the probability that an attempt would have been successful. Several deterrence rationales justifying the punishment of an attempt are described, & incentives to alter criminal conduct while commiting an attempt are discussed.