Background, study purpose and implementation - NERCHA, MOHSW, UNAIDS and GAMET/World Bank are collaborating in a capacity development process to support an evidence-based review of Swaziland’s epidemiological situation (coined Know your epidemic, KYE) and the national HIV prevention response (Know your response, KYR). The purpose of this modes of transmission (MoT) study is “to contribute to the ongoing efforts to understand the epidemic and response in Swaziland and thus help the country improve the scope (doing the right kind of activities), relevance (with the right populations) and comprehensiveness (reaching all members of target populations) of HIV prevention efforts”. The process described in this report entailed for the KYE part the in-depth review of available epidemiological data from Swaziland and the sub-region, as well as the application of the UNAIDS incidence model. The overall aim was to determine the epidemiology of new (incident) infections. The KYR part consisted of data collection regarding the policy context for prevention, strategic information on prevention and prevention activities by implementers, and the review of data from the National AIDS Spending Assessment (NASA) of 2008. In a final step, the KYE and KYR evidence was linked to produce an epidemic, response and policy synthesis with recommendations to improve the HIV prevention response through the evidence –informed alignment of prevention with the sources of new infections. The study examined the hypothesis that multiple, long-term heterosexual relationships, happening in a context of social norms, gender inequality and economic need, are a key contributor to the HIV transmission in Swaziland. Timing of the study - the MoT study took place at an opportune time since Swaziland was reviewing in the same time period the second national multisectoral HIV/AIDS strategic plan (2006-2008) and prepared for a new National Strategic Framework. The findings of the SDHS 2006-07, the NASA 2008 and the ‘Mapping of the National Minimum Package of HIV Services’ 2008 had just become available, and the MOHSW and NERCHA had established functional monitoring and evaluation (M&E) systems providing routine data, all providing essential input into the KYE and KYR analyses. Supervision and review - the study was overseen by the MoT Core Team through monthly meetings and progress reports. Dissemination of the findings and their translation into policy and practice is under the responsibility of the MoT Policy Team. Coordination and communication were ensured by the Coordinator of Communication & Advocacy of NERCHA and technical leadership was with GAMET/World Bank. The report has benefited from several reviews, conducted by the Swaziland Core Team, the Policy Team, Swaziland stakeholders, and regional peer reviewers (there were implementers of other MoT studies in Africa, UNAIDS RST ESA & UNAIDS Geneva, and GAMET/World Bank).