Judgments of whether a person is intoxicated by alcohol are important in a number of civil and law enforcement settings. This paper reviews how well people are able to make such judgments, the evidence for individual signs of intoxication, several structured rating techniques, and the use of sobriety tests. It is concluded that observers relying on common-sense clues of intoxication have limited ability to assess the blood alcohol concentration (BAC) levels of strangers, particularly below .10%. This generalization holds across professions that might be expected to show greater accuracy. Structured assessment instruments based on observable signs have shown promise but are confounded by the wide variations between casual social drinkers and those that have obtained a high level of tolerance. Among sobriety tests, only NHTSA's Standardized Field Sobriety Tests (SFSTs) have substantial, but seriously flawed, research support. Assessing the sobriety of strangers in the low to moderate BAC ranges without resort to chemical tests remains a daunting task. Copyright © 2010 John Wiley & Sons, Ltd.