AbstractThe scientific discipline called dendrochronology is the study of tree rings and of environmental conditions and events of the past that tree growth can reflect. The beginning of scientific study of tree rings is generally ascribed to an astronomer named Andrew Ellicott Douglass, who in the early 1900s noticed not only variation in tree‐ring width but also that this variability was similar between multiple trees. Dendrochronology subsequently expanded worldwide, and now over 3000 of the 12,000+ publications on dendrochronology can be classified as dendroclimatology. As a subfield of tree‐ring analysis, dendroclimatology estimates climate back in time beyond the start of recorded meteorological measurements. Dendroclimatology starts with site and tree selection and continues with dating, measuring, data quality control, and chronology construction. Tree rings are associated with climate using statistical models that are then evaluated for their full length to reconstruct climate of the past. Most commonly, either precipitation or temperature is reconstructed, and reconstructions are then analyzed for frequency of extreme years, changes in mean conditions, ranges of long‐term variability, and changes in interannual variability. For example, from reconstructions of Northern Hemisphere temperature based on tree rings and other natural archives of climate collected from multiple sites, it appears that current temperature (since ad 1850) exceeds the range of variability reconstructed for ad 1000‐1850. Uncertainties in dendroclimatology exist, including a relatively recent issue called divergence, but dendroclimatology has played, and continues to play, a substantial role in interdisciplinary research on climate change. Copyright © 2010 John Wiley & Sons, Ltd.This article is categorized under: Paleoclimates and Current Trends > Paleoclimate