The value of HIV testing has grown in parallel with the development of increasingly effective HIV treatment. Evidence for the substantial reductions in transmission when persons receive antiretroviral therapy creates a new impetus to increase testing and early diagnosis. Models of treatment as prevention--dubbed "test and treat"--give reason for optimism that control and elimination of HIV may now be within reach. This will be possible only with widespread testing, prompt and accurate diagnosis, and universal access to immediate antiviral therapy. Many successful approaches for scaling up testing were pioneered in resource-limited countries before they were adopted by countries in the developed world. The future of HIV testing is changing. Lessons learned from other case-finding initiatives can help chart the course for comparable HIV testing endeavors.