Impaired control over drinking has occupied a central place in explanations of alcohol dependence since the late 18th century. Despite this key theoretical role, no instrument has been developed to directly assess the construct. This article describes the development of a three-part Impaired Control Scale (ICS), in which Part 1 measures the degree to which a subject has attempted to exercise control over drinking in the past 6 months; Part 2 measures the degree of success in controlling drinking over the past 6 months; and Part 3 measures the subject's belief in his or her ability to control drinking if it were attempted. Psychometric analysis showed that, despite difficulties reported in the literature, impaired control could be measured in a reliable fashion, with satisfactory discriminant and concurrent validity. Preliminary investigation of the relationship between the ICS and elements of the alcohol dependence syndrome suggests that the construct of impaired control is related to, but may be distinguished from, a general factor of alcohol dependence. While more research is needed to replicate these findings and to examine interrelationships among the various parts of the ICS, the scale may have both theoretical and practical value in research and treatment for alcohol dependence and its related problems.