Since the early 1990s the Global Historical Climatology Network-Monthly (GHCN-M) data set has been an internationally recognized source of data for the study of observed variability and change in land surface temperature. It provides monthly mean temperature data for 7280 stations from 226 countries and territories, ongoing monthly updates of more than 2000 stations to support monitoring of current and evolving climate conditions, and homogeneity adjustments to remove non-climatic influences that can bias the observed temperature record. The release of version 3 monthly mean temperature data marks the first major revision to this data set in over ten years. It introduces a number of improvements and changes that include consolidating “duplicate” series, updating records from recent decades, and the use of new approaches to homogenization and quality assurance. Although the underlying structure of the data set is significantly different than version 2, conclusions regarding the rate of warming in global land surface temperature are largely unchanged.