Estimates of first-time drug use, referred to as incidence or initiation, provide an important measure of the Nation’s drug use problem. Marijuana is seen as the most widely used illicit drug in the Nation and in most cases the first illicit drug used by individuals. Based on data from the 1999 and 2000 National Household Surveys on Drug Abuse (NHSDAs), this report contains an analysis of the initiation of marijuana use. The goals of the report are to estimate incidence rates and trends of marijuana use, provide State-specific incidence estimates, identify characteristics and predictors of recent marijuana initiates, and examine the relationship between early marijuana use and later drug use patterns. The report is organized into seven chapters and covers data sources, variables and statistical methods, trends in marijuana incidence, State incidence estimates, characteristics of recent marijuana initiates, and early marijuana use and later drug use patterns. Data indicated a decrease in the rate of new marijuana use in 1999. Youths’ aged 15 to 17 had the highest rate of becoming new marijuana users in recent years. Whites were less likely than Blacks to start to use marijuana recently, and young American Indians/Alaska Natives appeared to have an elevated risk of becoming new marijuana users in recent years. Future analysis of the NHSDA data was suggested as helping to confirm the findings from the 1999 and 2000 surveys and to track changes in the trend of new marijuana use by at-risk subgroups. Tables, figures, references, and appendices A-C