This article reviews how the Nordic countries of Denmark, Finland, Norway, and Sweden enforce their legislation pertaining to driving under the influence of alcohol and/or other impairing drugs. The evidence necessary for a successful prosecution of traffic offenders has undergone radical changes over the past 50 years. The once widely used clinical tests of impairment are no longer a major element of the prosecution case and a physician is more seldom required to examine apprehended drivers and document any clinical signs and symptoms of alcohol and/or drug influence. These clinical tests have been superseded by results derived from a comprehensive toxicological analysis of psychoactive substances in samples of the driver's blood. The current statutory limits of blood-alcohol concentration (BAC) are among the lowest in the world: Norway and Sweden (0.20 g/kg) and Denmark and Finland (0.50 g/kg). Results from using evidential quality breath-alcohol instruments are accepted as evidence in drunk-driving cases and this has necessitated setting statutory breath-alcohol concentration (BrAC) limits. Laws dealing with driving under the influence of drugs (DUID) other than alcohol have also been updated and made more pragmatic for prosecution of traffic offenders. In Finland and Sweden zero-tolerance laws exist, making it illegal to drive with any quantifiable amount of a scheduled drug in the driver's blood. Prescription drugs are exempt from this zero-tolerance mandate provided the medication was used in accordance with a physician's ordination. Lacking a valid prescription or if there is a supratherapeutic concentration of the drug in blood, this will lead to a prosecution for DUID. In Denmark and Norway threshold concentration limits have been established for many psychoactive drugs, both licit and illicit. After these stricter laws for DUID were introduced, the number of suspects apprehended by the police per year increased by as much as tenfold in some Nordic countries. There is increasing evidence that many traffic delinquents in the Nordic countries suffer from a substance-use disorder, because repeat-offending is a common occurrence. This suggests that some type of treatment and rehabilitation program might be more beneficial compared with conventional penalties for people arrested for DUI and/or DUID.