Men who have sex with men still comprise most new HIV cases in Australia. Condoms were the main HIV risk reduction strategy used for most of the HIV epidemic. Over the past decade, gay and bisexual men (GBM) have adopted a range of HIV risk reduction strategies, including PrEP. These changes have shifted HIV prevention norms in place for decades. In this thesis, I set out to understand how these changes affected how GBM negotiated sex and HIV risk, with a particular focus on GBM who struggle to use an effective HIV prevention method, despite the broader range available. A community-based, social public health approach was taken, with a focus on understanding the impact of PrEP practices and recommendations to improve health promotion. National survey data were analysed on changing attitudes to condoms among GBM. Cohort study data were used to identify the characteristics of GBM who did not consistently use HIV risk reduction strategies. Qualitative interviews were undertaken with GBM in Sydney to explore why some do not use a HIV risk reduction strategy and changing practices of HIV and PrEP disclosure. The survey data found consistently negative attitudes towards condoms among GBM and that it had become harder to discuss condom use with partners as PrEP use increased. Men who did not consistently use any HIV prevention strategy were younger, less educated, preferred receptive anal intercourse, and were less socially engaged with GBM. In qualitative analysis, the characteristics of encounters that featured little or no HIV risk reduction included: familiarity and trusting partners; pleasure and intoxication; expectations that partners were using PrEP or HIV treatment as prevention; and sometimes feelings of inevitability about acquiring HIV. In the context of increasing PrEP use, clear expectations about HIV and PrEP disclosure had not yet emerged, with some GBM only disclosing online and others not at all. The rapid uptake of PrEP has changed the way that GBM negotiate sex and HIV risk. As condoms have become harder to discuss with partners and no clear norms about PrEP disclosure have yet emerged, negotiating risk has become more complicated. GBM not using any HIV risk reduction strategy should be supported to adopt one compatible with situations in which they experience risk. This is important to increase community knowledge about effective HIV prevention strategies and support GBM to negotiate sex when there are no clear norms or expectations about disclosure.