Defining who is in the nonprofit sector, and where they sit within that sector, is a powerful task. Any attempt to do it at an international scale must recognize the diversity of voluntary activity and civil society across cultures and contexts. In this chapter, we consider the challenges of applying classifications in different cultures, before going on to explore both the opportunities and challenges that new data and technologies offer for complex classification at scale. We conclude with some reflections on how the theory and application of classification might proceed in the future.