Since bumblebees are a group associated with cool climates, Britain supports a large proportion (~10%) of the world's bumblebee fauna. However, three of our 25 species have become extinct, and seven species are Biodiversity Action Plan (BAP) listed, a higher proportion than for any other insect group. Declines are primarily driven by habitat loss and declines in floral abundance resulting from agricultural intensification, notably the loss of ~97% of all species-rich grasslands (haymeadows, calcareous grasslands) in the last 60 years. The decline in the abundance of Red Clover, once a common fodder and ley crop and a major source of pollen and nectar for many bumblebee species, is likely to have had a significant impact. Effects of habitat degradation and fragmentation are compounded by the social nature of bumblebees and by their largely monogamous breeding system, which means that they have a very low effective population size (most bumblebees are sterile workers). Hence, populations are susceptible to chance extinction events and inbreeding. Given the importance of bumblebees as pollinators of crops and wildflowers, their declines have broad ecological and economic significance. Suggested measures for their conservation include tight regulation of commercial bumblebee use and targeted use of agri-environment schemes to enhance floristic diversity in agricultural landscapes.