The impact of poor menstrual hygiene management (MHM) on women's and girls' participation in education and income generation in the Pacific, a sub-region with the world's lowest water, sanitation and hygiene (WASH) coverage, is poorly understood. Globally and regionally there is limited research on MHM beyond school settings, particularly among marginalized women. In 2016 the Australian Department of Foreign Affairs and Trade commissioned research in three Pacific nations to inform regional MHM programming. A multi-country mixed-methods study was undertaken in rural and urban sites in Papua New Guinea (PNG), Solomon Islands (SI) and Fiji, to examine barriers to women's and girls' effective MHM and impacts on their participation in education and income generation. 293 women, men and adolescent girls, including women working in informal economies and women with disabilities, participated in focus group discussions and interviews. Structured observations of WASH facilities were undertaken in schools and workplaces alongside an analysis of the availability, cost and quality of sanitary products. Menstruation-related beliefs differed across the three settings and were perceived to be a barrier to effective MHM, particularly in PNG and SI. As an upper-middle income country, Fiji has made greater progress in addressing MHM. Women working in informal economies in rural and urban areas in all three countries faced the greatest challenges managing MHM due to lack of access and affordability of quality sanitary products, the poor functionality of WASH facilities and associated user fees (where applicable). MHM challenges were compounded for those living in rural and remote areas and for those with a disability, and were related to accessibility/affordability of quality sanitary products, adequate information and functional WASH facilities. These challenges contribute to absenteeism from school and work. Across all countries, most adolescent girls aspired to use disposable sanitary products. This study informs approaches to improving MHM in the Pacific. It highlights the need for MHM solutions to address disparities between urban and rural populations, among women and girls working in informal settings and those experiencing disability. The preference by some women and most girls to use disposable products, despite widespread affordability and quality issues in rural and some urban areas, and a lack of effective, at-scale solid waste management systems make the issue of product alone a critical one. Meanwhile cultural beliefs that menstrual blood is 'dirty' remain a barrier to effective MHM for many women and girls. Poor MHM in SI, PNG and Fiji will remain a barrier to gender equality in each country without context-appropriate, crosssectoral collaboration, that addresses areas of unmet need and focusses attention on the most marginalised. Most importantly the research findings call for women and girls to be at the centre of all solutions.