By every measure, the prevalence of need for substance abuse treatment is many times greater among offenders than in the general population. As used in this article, the "demand" for substance abuse treatment consists of three components: those receiving treatment, those referred to or seeking treatment but not receiving it, and others who would accept treatment if offered or mandated to them. In all of these components, the "need" for treatment is an implicit criterion. This article focuses on the factors that influence potential demand for substance abuse treatment in the criminal justice system. The factors are placed under the following categories: treatment access factors, readiness for treatment, attitudes toward treatment, attitudes toward the criminal justice system intervention coupled with treatment, attitudes toward incarceration, procedural posture, and the credibility of threats. In setting an agenda for research on new measurements of treatment need and demand, this article poses four questions for research consideration. First, what is the need for treatment among offenders by level of treatment; second, by level, how much active treatment demand is being met; third, among those offenders who need treatment but are not currently seeking it, how many will enter treatment at the appropriate level if they face sanctions consistent with the seriousness of their crime and the weight of their prior criminal record; and fourth, how do personal characteristics and circumstances affect offenders' choices between treatment and incarceration, and can these data be used to make cross-jurisdiction population estimates of potential demand? 2 tables, 6 notes, and 54 references