Since the establishment of the first drug court in Dade County in 1989, the growth of treatment drug courts in the United States has been extraordinary. Due to the innovation of such courts proceeding well ahead of findings regarding their impact, an important research task involved capturing the experiential base and practical knowledge generated by older drug courts as problems have been identified and addressed. This article focused on one aspect of a larger retrospective evaluation of two of the nation’s pioneering drug courts in Clark County (Las Vegas), Nevada, and Multnomah County (Portland), Oregon, funded by the National Institute of Justice. This article considered the influence of important contextual factors, such as political, administrative, and policy changes in explaining the evolution of drug courts as dynamic innovations. The article illustrated the importance of considering the influence of contextual factors in shaping the drug court mechanism that delivers treatment to participants whose performance forms the principal basis of outcome evaluations. The analyses focused on two stages of enrollment as appropriate tests of the influence of outside factors: (1) the initial screening or orientation stage, and (2) the subsequent enrollment state, beginning the drug court process. The targeted populations for the drug courts principally involved felony drug defendants. The time series analyses suggested that several contextual factors played an important role in shaping these courts and affecting their impact on the target populations. The analyses of screening and enrollment as indicators of drug court implementation over time identified patterns in enrollments that were not simply explained by fluctuations in drug arrests by local police. These findings illustrated the dynamic contexts within which these two drug courts have developed and functioned and provided a sense of the historical framework within which the evaluation findings related to impact and performance should be viewed. With the growth of drug courts, the model itself has not remained static. It has evolved and diversified across the Nation. Drug courts have been forced to adapt to changes in Federal and State law, politics, general court policy and leadership, and changes in their clients, both in terms of their drug use and needs. Tables and references