This report provides information on the demographic and substance abuse characteristics of the 1.8 million annual admissions to treatment for abuse of alcohol and/or drugs in facilities that report to individual, State administrative data systems. The TEDS system comprises two major components: the Admissions Data Set and the Discharge Data Set. The TEDS Admissions Data Set is an established (15 years) program that includes data on treatment admission routinely collected by States to monitor their individual substance abuse treatment systems. The TEDS Discharge Data Set is more recently established, with the first data reported for 2000. For both datasets, selected data items from the individual State data files are converted to a standardized format consistent across States. These standardized data constitute TEDS. The TEDS Admissions Data System consists of a Minimum Data Set collected by all States, and a Supplemental Data Set collected by some States. The Minimum Data Set consists of 19 items, including demographic information; primary, secondary, and tertiary substances and their route of administration, frequency of use, and age at first use; source of referral to treatment; number of prior treatment episodes; and service type, including planned use of medication, such as assisted opioid therapy. The Supplemental Data Set consists of 15 items involving psychiatric, social, and economic measures. The TEDS Discharge Data System enables TEDS to collect information on entire treatment episodes. Discharge data, when linked to admissions data, represent treatment episodes that enable analyses of questions that cannot be answered with admissions data alone. Tables, figures