In a systematic review and meta-analysis, Amitabh Suthar and colleagues describe the evidence base for different HIV testing and counseling services provided outside of health facilities. Please see later in the article for the Editors' Summary, Background Effective national and global HIV responses require a significant expansion of HIV testing and counselling (HTC) to expand access to prevention and care. Facility-based HTC, while essential, is unlikely to meet national and global targets on its own. This article systematically reviews the evidence for community-based HTC. Methods and Findings PubMed was searched on 4 March 2013, clinical trial registries were searched on 3 September 2012, and Embase and the World Health Organization Global Index Medicus were searched on 10 April 2012 for studies including community-based HTC (i.e., HTC outside of health facilities). Randomised controlled trials, and observational studies were eligible if they included a community-based testing approach and reported one or more of the following outcomes: uptake, proportion receiving their first HIV test, CD4 value at diagnosis, linkage to care, HIV positivity rate, HTC coverage, HIV incidence, or cost per person tested (outcomes are defined fully in the text). The following community-based HTC approaches were reviewed: (1) door-to-door testing (systematically offering HTC to homes in a catchment area), (2) mobile testing for the general population (offering HTC via a mobile HTC service), (3) index testing (offering HTC to household members of people with HIV and persons who may have been exposed to HIV), (4) mobile testing for men who have sex with men, (5) mobile testing for people who inject drugs, (6) mobile testing for female sex workers, (7) mobile testing for adolescents, (8) self-testing, (9) workplace HTC, (10) church-based HTC, and (11) school-based HTC. The Newcastle-Ottawa Quality Assessment Scale and the Cochrane Collaboration's “risk of bias” tool were used to assess the risk of bias in studies with a comparator arm included in pooled estimates. 117 studies, including 864,651 participants completing HTC, met the inclusion criteria. The percentage of people offered community-based HTC who accepted HTC was as follows: index testing, 88% of 12,052 participants; self-testing, 87% of 1,839 participants; mobile testing, 87% of 79,475 participants; door-to-door testing, 80% of 555,267 participants; workplace testing, 67% of 62,406 participants; and school-based testing, 62% of 2,593 participants. Mobile HTC uptake among key populations (men who have sex with men, people who inject drugs, female sex workers, and adolescents) ranged from 9% to 100% (among 41,110 participants across studies), with heterogeneity related to how testing was offered. Community-based approaches increased HTC uptake (relative risk [RR] 10.65, 95% confidence interval [CI] 6.27–18.08), the proportion of first-time testers (RR 1.23, 95% CI 1.06–1.42), and the proportion of participants with CD4 counts above 350 cells/µl (RR 1.42, 95% CI 1.16–1.74), and obtained a lower positivity rate (RR 0.59, 95% CI 0.37–0.96), relative to facility-based approaches. 80% (95% CI 75%–85%) of 5,832 community-based HTC participants obtained a CD4 measurement following HIV diagnosis, and 73% (95% CI 61%–85%) of 527 community-based HTC participants initiated antiretroviral therapy following a CD4 measurement indicating eligibility. The data on linking participants without HIV to prevention services were limited. In low- and middle-income countries, the cost per person tested ranged from US$2–US$126. At the population level, community-based HTC increased HTC coverage (RR 7.07, 95% CI 3.52–14.22) and reduced HIV incidence (RR 0.86, 95% CI 0.73–1.02), although the incidence reduction lacked statistical significance. No studies reported any harm arising as a result of having been tested. Conclusions Community-based HTC achieved high rates of HTC uptake, reached people with high CD4 counts, and linked people to care. It also obtained a lower HIV positivity rate relative to facility-based approaches. Further research is needed to further improve acceptability of community-based HTC for key populations. HIV programmes should offer community-based HTC linked to prevention and care, in addition to facility-based HTC, to support increased access to HIV prevention, care, and treatment. Review Registration International Prospective Register of Systematic Reviews CRD42012002554 Please see later in the article for the Editors' Summary, Editors' Summary Background Three decades into the AIDS epidemic, about 34 million people (most living in resource-limited countries) are infected with HIV, the virus that causes AIDS. Every year another 2.2 million people become infected with HIV, usually through unprotected sex with an infected partner, and about 1.7 million people die. Infection with HIV, which gradually destroys the CD4 lymphocytes and other immune system cells that provide protection from life-threatening infections, is usually diagnosed by looking for antibodies to HIV in the blood or saliva. Disease progression is subsequently monitored in HIV-positive individuals by counting the CD4 cells in their blood. Initiation of antiretroviral drug therapy—a combination of drugs that keeps HIV replication in check but that does not cure the infection—is recommended when an individual's CD4 count falls below 500 cells/µl of blood or when he or she develops signs of severe or advanced disease, such as unusual infections. Why Was This Study Done? As part of intensified efforts to eliminate HIV/AIDS, United Nations member states recently set several HIV-related targets to be achieved by 2015, including reduced transmission of HIV and increased delivery of antiretroviral therapy. These targets can only be achieved if there is a large expansion in HIV testing and counseling (HTC) and increased access to HIV prevention and care services. The World Health Organization currently recommends that everyone attending a healthcare facility in regions where there is a generalized HIV epidemic (defined as when 1% or more of the general population is HIV-positive) should be offered HTC. However, many people rarely visit healthcare facilities, and others refuse “facility-based” HTC because they fear stigmatization and discrimination. Thus, facility-based HTC alone is unlikely to be sufficient to enable national and global HIV targets to be reached. In this systematic review and meta-analysis, the researchers evaluate the performance of community-based HTC approaches such as index testing (offering HTC to the sexual and injecting partners and household members of people with HIV), mobile testing (offering HTC through a service that visits shopping centers and other public facilities), and door-to-door testing (systematically offering HTC to homes in a catchment area). A systematic review uses predefined criteria to identify all the research on a given topic; meta-analysis combines the results of several studies. What Did the Researchers Do and Find? The researchers identified 117 studies (most undertaken in Africa and North America) involving 864,651 participants that evaluated community-based HTC approaches. Among these studies, the percentage of people offered community-based HTC who accepted it (HTC uptake) was 88% for index testing, 87% for self-testing, 80% for door-to-door testing, 67% for workplace testing, and 62% for school-based testing. Compared to facility-based approaches, community-based approaches increased the chances of an individual's CD4 count being above 350 cells/µl at diagnosis (an important observation because early diagnosis improves subsequent outcomes) but had a lower positivity rate, possibly because people with symptoms of HIV are more likely to visit healthcare facilities than healthy individuals. Importantly, 80% of participants in the community-based HTC studies had their CD4 count measured after HIV diagnosis, and 73% of the participants initiated antiretroviral therapy after their CD4 count fell below national eligibility criteria; both these observations suggest that community-based HTC successfully linked people to care. Finally, offering community-based HTC approaches in addition to facility-based approaches increased HTC coverage seven-fold at the population level. What Do These Findings Mean? These findings show that community-based HTC can achieve high HTC uptake rates and can reach HIV-positive individuals earlier, when they still have high CD4 counts. Importantly, they also suggest that the level of linkage to care of community-based HTC is similar to that of facility-based HTC. Although the lower positivity rate of community-based HTC approaches means that more people need to be tested with these approaches than with facility-based HTC to identify the same number of HIV-positive individuals, this downside of community-based HTC is likely to be offset by the earlier identification of HIV-positive individuals, which should improve life expectancy and reduce HIV transmission at the population level. Although further studies are needed to evaluate community-based HTC in other regions of the world, these findings suggest that offering community-based HTC in HIV programs in addition to facility-based testing should support the increased access to HIV prevention and care that is required for the intensification of HIV/AIDS elimination efforts. Additional Information Please access these websites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.1001496. The World Health Organization provides information on all aspects of HIV/AIDS, including information on counseling and testing (in several languages) Information is available from the US National Institute of Allergy and Infectious Diseases on HIV infection and AIDS NAM/aidsmap provides basic information about HIV/AIDS and summaries of recent research findings on HIV care and treatment Information is available from Avert, an international AIDS charity, on many aspects of HIV/AIDS, including information on the global HIV/AIDS epidemic, on HIV testing, and on HIV transmission and testing (in English and Spanish) The UK National Health Service Choices website provides information (including personal stories) about HIV and AIDS The World AIDS Day Report 2012 provides up-to-date information about the AIDS epidemic and efforts to halt it Patient stories about living with HIV/AIDS are available through Avert; the nonprofit website Healthtalkonline also provides personal stories about living with HIV, including stories about getting a diagnosis