Abstract HIV/AIDS is a global epidemic with the greatest burden in terms of prevalence, morbidity and mortality in sub-Saharan Africa, parts of Asia and, more recently, the Caribbean. Immigrants from these regions of birth now make up a significant proportion of people living with HIV in many high-income countries, including Australia. The higher priority accorded to people from culturally and linguistically diverse (CALD) backgrounds in Australian national and local HIV/AIDS strategies generates a broad question on ‘how’ to implement HIV prevention interventions with immigrants to address what are often atypical modes of HIV transmission and observed disparities in areas such as later presentation with HIV. HIV prevention in Australia has included whole-of-population approaches alongside targeted approaches, which address HIV prevention with specific groups – usually those disproportionately affected by HIV/AIDS such as gay men or injecting drug users. Targeted health promotion interventions for immigrants have also formed part of the HIV response in Australia. Immigrants in Australia may have acquired HIV prior to their first arrival in Australia, on subsequent travel abroad, or within Australia. A key gap in our evidence base in Australia includes what we can learn from interventions implemented in other high-income countries to guide new, or strengthen existing, approaches to culturally appropriate primary and secondary HIV prevention with immigrants locally. Typically it is taken as a given that prevention interventions will be more effective if they are culturally appropriate to the population they serve, and a range of strategies and activities are used to achieve this. However, there is rarely an examination of what mechanisms – the ‘change elements’ or program theories of the intervention – contribute to culturally appropriate interventions. This research, in the form of a realist review of evidence, sought to ‘unpack’ the mechanisms for achieving cultural appropriateness in HIV prevention interventions with immigrants that have been implemented in contexts similar to Australia. Thus the broad question the research sought to answer was ‘How and why do interventions work (or not), for which groups of immigrants, and in what contexts?’ The review of evidence in HIV prevention included a span of interventions from community-level approaches using mass media through to interventions delivered at a group level to immigrants. Systematic searches were carried out on major public health databases (PubMed, CINAHL, Sociological Abstracts, PsychInfo) and Google Scholar to find peer-reviewed and grey literature relevant to HIV prevention among immigrants. Two types of studies contributed to the review of evidence – studies of interventions and qualitative studies of immigrants’ views on HIV/AIDS prevention – in order to bring together ‘expert’ and ‘lay’ understandings of HIV prevention among immigrants. Simultaneously, a scan of the literature mapped preliminary mechanisms contributing to cultural appropriateness in HIV prevention interventions with immigrants. This preliminary set of seven mechanisms – ‘authenticity’, ‘understanding’, ‘consonance’, ‘specificity’, ‘embeddedness’, ’endorsement’ and ‘framing’ – were theorised as the key, rather than the only, interrelated mechanisms contributing to cultural appropriateness in interventions with immigrants. These preliminary mechanisms were then tested, revised and refined against evidence – 74 ‘grey’ and peer-reviewed studies and reports relevant to HIV prevention with immigrants – found in systematic searches. The evidence indicates that the pivotal mechanisms contributing to cultural appropriateness in HIV prevention interventions with immigrants are ‘understanding’ and ‘consonance’ – ensuring that language (usually the ‘mother tongue’) and cultural values are included as key elements in the development and implementation of the intervention. ‘Authenticity’, ‘specificity’ and ‘embeddedness’were moderately important in contributing to cultural appropriateness – mechanisms that dealt with staffing, targeting through ethnicity and using settings for interventions – from the evidence included in the review. Finally, there was mixed evidence for the roles of ‘endorsement’ and ‘framing’, which suggests that gaining community endorsement or partnering initiatives with immigrants or immigrant community institutions were the least critical mechanisms in contributing to cultural appropriateness in terms of HIV prevention interventions. Further research is needed to examine the relationships between these seven mechanisms and any impacts they contribute to the effectiveness of interventions and HIV-related health outcomes among immigrants.