Bumble bees are important pollinators of both wild and cultivated plants, and worldwide, many species are reported to be in decline. California is a hotspot for bumble bee biodiversity, with more than half of North American species occurring in the state, including several near-endemics. The state also features many of the stressors thought to be driving bumble bee declines, including agricultural intensification, loss of habitat to development, and climate change-related ecological disturbance. California has a rich history of entomological research, including both historical specimen collections and recent community science observations. However, the state has never had a standardized inventory of these functionally important insects. In this talk, we summarize the current state of knowledge of California’s native bumble bees, and discuss how a systematic community science survey effort, the California Bumble Bee Atlas, will address information gaps, ultimately informing conservation action throughout the state. Significantly, the project will clarify the current distributions of several imperiled species, including Bombus crotchii, B. franklini, and B. occidentalis, and will result in a baseline dataset that will assist in ongoing and future efforts to protect California bumble bee populations and the pollination service they provide to agriculture and native plant communities.