Glaciers are iconic elements of the heritage of several mountain UNESCO biosphere reserves (BR). Although such site designations bring benefits, notably the embedded role of communities in site management, glaciers remain highly susceptible to the effects of climate change. Several monitoring studies have shown a global retreat of glaciers, at an unprecedented rate of mass loss. As has been long-established, this rapid retreat is impacting not only ecological and hydrological dynamics of mountain regions, but local communities that benefit from their ecosystem services. Here we present the first comprehensive inventory of glaciated areas within the World Network of Mountain Biosphere Reserves (WNMBR), identifying BRs containing glacier across all global mountain regions. For all BRs with suitable geospatial extent information, we quantified glacier areas using the latest Randolph Glacier Inventory (RGI) (v7.0). This was done for both entire BRs and, where possible, their sub-zones. Our work yields a first-order assessment of glacier importance both within and between BRs globally. We highlight both benefits and limitations of the available spatial glacier and BR extent data for such a global yet localised assessment. For instance, the Randolph Glacier Inventory (RGI) has good global coverage, but glacier outlines relate to the year 2000 (considerable change has occurred since then). Moreover, standardised digital cartography of BRs remains lacking. These results emphasise the need to develop a unified approach to BR spatial data development that balances scientific rigor with practical implementation constraints faced by biosphere reserve managers. The study concludes by proposing a collaborative framework through which biosphere reserve stakeholders can contribute local field observations to establish and maintain an updated and more accurate BR glacier inventory to provide a valuable foundation for future climate adaptation strategies in mountain regions worldwide.