The Census of Marine Life is a sweeping 10-year effort to catalog life in the ocean. Four of its fourteen field projects focus on the tiniest sea creatures—microbes, larvae, zooplankton, and burrowers—which are the most numerous of marine species. In fact, the number of microbial species in the ocean is estimated to be 1,000 times greater than the rest of the planet's known biodiversity. This Bio Bulletin highlights this research effort in celebration of the International Year of Biodiversity.