In order to make a lawful arrest for drunk driving, there must be "probable cause" to believe that the driver has violated the drunk driving statute. ''Probable cause'' exists when the facts and circumstances within the officer's knowledge at the time of the arrest are sufficient to warrant the belief by a reasonable and prudent person that an offense has been committed. Probable cause must be based on objective facts and circumstances and not upon the personal opinions or suspicions of the officer. Further, probable cause must exist at the moment of police action and not thereafter.

In most jurisdictions, courts have found that the obvious symptoms of intoxication constitute sufficient probable cause for an officer to arrest and charge a motorist with driving under the influence of intoxicating liquor. These may include watery and bloodshot eyes, flushed face, slurred speech, an odor of alcohol emanating from the motorist's breath or person, and an inability to perform field sobriety tests. Because the statutes of most states permit a warrantless arrest for offenses committed in the presence of an officer, as does the common law, the officer must be "present" or "in view" of the motorist at the time he or she was allegedly driving while under the influence of intoxicating liquor. Courts have been liberally construed these terms, however.

Although probable cause to believe that the driver has violated the drunk driving statute is necessary for a lawful arrest for drunk driving, it is not necessary for a lawful initial stop of a driver. However, after effecting a lawful stop, if the officer suspects that the motorist is intoxicated, the officer may request the driver to perform a series of field sobriety tests designed to measure coordination, balance, and dexterity. Most states only require that a police officer have reasonable suspicion that an individual is driving under the influence before conducting field sobriety tests. A few states, however, require that the more stringent standard of "probable cause" must first exist before requesting field sobriety tests. In any event, the results of field sobriety tests are inadmissible into evidence in any civil or criminal proceeding unless there has been an arrest for drunk driving.