There is now compelling evidence that harm reduction approaches to HIV prevention among injecting drug users are effective, safe and cost-effective. The evidence of effectiveness is strongest for needle and syringe programs and opioid substitution treatment. There is no convincing evidence that needle and syringe programs increase injecting drug use. The low prevalence (~1%) of HIV among injecting drug users reflects the early adoption and rapid expansion of harm reduction in Australia. Countries that have provided extensive needle and syringe programs and opioid substitution treatment appear to have averted an epidemic, stabilised or substantially reduced the prevalence of HIV among injecting drug users. However, despite decades of vigorous advocacy and scientific evidence, the global coverage of needle and syringe programs and opioid substitution treatment falls well short of the levels required to achieve international HIV control.