The Diatom Paleolimnology Data Cooperative (DPDC) is a web-accessible database of diatom and associated ecological and paleolimnological data relevant to study of global change. It contains data on regional surface-sample calibration sets (counts, water chemistry, inference models), sediment cores (counts, dating information, and diatom inferred characteristics), and other types of samples. It is intended for researchers needing data on long-term trends in variables related to global change, and diatomists involved with creating those data. Initial emphasis has been on data sets providing information on salinity, lake level, hydrology, trophic state, pH, and other factors that can be related to climate change, acidic deposition and eutrophication.