There has been limited research on illicit drug distribution in prisons in England, mainly due to methodological problems in collecting this type of information. The current study was one facet of the Supply Reduction Program initiated by the Prison Service Drug Strategy Unit in February 2003. The study involved in-depth interviews with 121 serving and recently released prisoners as well as 37 staff from 5 male prisons and 1 female prison in England. Prisoner and ex-prisoner participants were selected on the basis of their knowledge of drug use in prison. Other data collected for analysis included information from mandatory drug testing (MDT) and drug-related security information reports (SIRs). Results indicated that 79 percent of prisoner participants in all six prisons reported using illicit drugs during their most recent imprisonment, with more than half of these respondents reporting frequent use of drugs such as heroin and cannabis. Different levels of drug distribution networks were reported, with evidence of more organized distribution in some of the prisons. Drug treatment programs varied, with the variance in programming impacting prisoners’ decisions on whether to use drugs in prison. Six main routes of drug supply into prisons were reported: via social visits, mail, new receptions, prison staff, over the perimeter wall or fence, and via reception after court visits. Prisoners obtained drugs through six main payment methods: canteen items, outside payment, personal property, swapping other drugs, providing services, and cash. Recommendations are offered for both drug treatment strategies and for anti-drug supply security. Tables, figures, references, and annex