Fishermen are a high-risk group for HIV, having higher HIV rates than typically high-risk groups like truck drivers and military personnel (Kissling, et al., 2005a). Despite this, fishing communities have consistently fallen through the net of HIV research initiatives and in Southeast Asia, there are few such projects targeting fishermen and their communities. In Malaysia, there is particular cause for concern as estimates suggest that fishing communities have an HIV prevalence rate 10 times that of the general population (Kissling, et al., 2005a). Although only 1.3% of the working population are employed in the fishing industry (Department of Statistics Malaysia, 2005), fishermen constitute 3.8% of the total reported HIV cases in the country (Ministry of Health Malaysia, 2008). The dearth of research initiatives targeting HIV within Malaysian fishing communities, and the criminalization of drug users, more broadly, underscores the need for a greater understanding of why fishermen are at increased risk for HIV, but also what approaches might be most effective at curbing the HIV epidemic for these men. This research examines HIV among fishermen by focusing on the social drivers of drug use and drug-related risk behavior in this community. Drawing on theories of risk, this research employs an approach that situates HIV risk behavior within the larger social context. Specifically, I ask: what social factors support an environment conducive to risk behavior and the transmission of HIV among this population of fishermen? Using a mixed-methods approach, this dissertation examines multi-level determinants of HIV among fishermen in Malaysia, assessing how occupational characteristics, social networks, and conceptions of masculinity shape drug use and HIV risk behaviors. The focus on occupational characteristics contributes to the literature on occupational cultures and workplaces as sites for the production of health vulnerabilities, particularly HIV. The focus on masculinity speaks to the to need to better understand the cultural meanings and gender norms associated with HIV risk behaviors among men and the attention to social networks complements a growing body of research that recognizes the role of informal networks in amplifying or attenuating health-related risk. The data for this dissertation comes from Project WAVES, a study conducted by the University of Malaya in collaboration with the Social Intervention Group at Columbia University. The study was conducted in and around the Kuantan jetty, one of the busiest fishing jetties in the country, located in Pahang State on the east coast of peninsular Malaysia. The data consist of 28 in-depth semi-structured interviews with drug-using fishermen and survey data from 406 fishermen who were recruited using respondent-driven sampling. The findings of this research suggest that multilevel factors tied to occupational structure shaped drug use and risk behavior contexts. The mechanization of the fishing industry created shifts in the local labor market that shaped fishermen's daily work and lives. In this new occupational context, the social and economic organization of the occupation of fishing supported drug use in this community. In particular, boat captains loaned money to buy drugs and some supplied drugs for the purpose of work, which resulted in unsafe injection practices and more limited access to clean needles/syringes. The integration of drug use and drug users into the occupational culture of fishing also shaped social and drug-using networks. I find that multidimensional aspects of social network relationships, including social support, trust, participation, and isolation were significantly associated, both positively and negatively, with recent injection and sharing needles/syringes. The results also demonstrate connections between masculinity and injection-related HIV risk behavior. Of note, drug using men were marginalized in their communities and drug use posed a threat to masculinity as men who used drugs were seen as "less of a man" or lacking in "reason." When this marginalization was internalized, men were more likely to engage in receptive sharing of a needle/syringe. Collectively, these results indicate that occupational characteristics, networks and masculinity intersect in complex ways to increase drug use and HIV among fishermen in Kuantan. Although the findings highlight a number challenges to reducing HIV in this population, they also point to a number of possible interventions, which are discussed in the final chapter.