Establishing protected areas (PAs) ranks among the top priority actions to mitigate the global scale of modern biodiversity declines. However, the distribution of biodiversity is spatially asymmetric among regions and lineages, and the extent to which PAs offer effective protection for species and ecosystems remains uncertain. Penguins, regarded as prime bioindicator birds of the ecological health of their terrestrial and marine habitats, represent priority targets for such quantitative assessments. Of the world's 18 penguin species, eleven are undergoing population declines, of which ten are classified as 'Vulnerable' or 'Endangered'. Here, we employ a globalscale dataset to quantify the extent to which their terrestrial breeding areas are currently protected by PAs. Using quantitative methods for spatial ecology, we compared the global distribution of penguin colonies, including range and population size analyses, with the distribution of terrestrial PAs classified by the International Union for Conservation of Nature, and generated hotspot and endemism maps worldwide. Our assessment quantitatively reveals <40% of the terrestrial range of eleven penguin species is currently protected, and that range size is the significant factor in determining PA protection. We also show that there are seven global hotspots of penguin biodiversity where four or five penguin species breed. We suggest that future penguin conservation initiatives should be implemented based on more comprehensive, quantitative assessments of the multi-dimensional interactions between areas and species to further the effectiveness of PA networks.