Hundreds of small-scale experiments have shown that ecosystem functions and services, including pollination, increase with the number of species providing them. On this basis, the maintenance of ecosystem services has become a cornerstone argument for the preservation of biodiversity globally. However, ecologists actually know rather little about how the biodiversity-function relationship works in real-world ecosystems. In this talk I identify the big questions about biodiversity and ecosystem services that remain to be answered at large scales, and how the answers might be systematically different from those already known from smaller scales. I organize my argument around the results of landscape-scale research on pollinators and pollination, as the study system making the single greatest contribution to this field.