Drug use in the workplace, its effect on performance and safety, and the role of workplace drug testing has received much attention in the popular press. But what do we actually know about this troubling issue? With an extensive and readable overview of the literature, the committee presents what we do know by examining the major issues: the extent and severity of drug use on and off the job; the strengths and weaknesses of methods for detecting drug use through standard drug tests; the effect of drug use on behavior, including the results of both laboratory and field studies that have examined work-related behavior and worker productivity; and the effectiveness of interventions to deal with drug use, such as employee assistance programs, health promotion programs, and treatment programs for substance abuse. This volume will be of practical interest to human resource and employee assistance program managers, policymakers, and investigators.