This paper reviews evidence for climate change over the past several millennia, focusing on changes over the past 1 to 2 millennia. The authors assess reconstructions and modeling studies analyzing various climate fields, including atmospheric circulation diagnostics, precipitation, and drought. They emphasize proxy-based reconstructions of temperature patterns in past centuries, which place recent large-scale warming in a longer-term context. The assessment confirms that late 20th-century warmth is unprecedented at hemispheric and likely global scales. There is more tentative evidence that certain climate variability modes, such as the El Niño/Southern Oscillation and the North Atlantic Oscillation, may have exhibited late 20th-century behavior that is anomalous in a long-term context. Regional conclusions, particularly for the Southern Hemisphere and parts of the tropics where high-resolution proxy data are sparse, are more circumspect. The paper highlights the limited utility of terms like the "Little Ice Age" and "Medieval Warm Period" for describing past climate epochs. Comparison of empirical evidence with proxy-based reconstructions shows that natural factors explain relatively well the major surface temperature changes of the past millennium through the 19th century, while anthropogenic forcing can explain the recent anomalous warming in the late 20th century.This paper reviews evidence for climate change over the past several millennia, focusing on changes over the past 1 to 2 millennia. The authors assess reconstructions and modeling studies analyzing various climate fields, including atmospheric circulation diagnostics, precipitation, and drought. They emphasize proxy-based reconstructions of temperature patterns in past centuries, which place recent large-scale warming in a longer-term context. The assessment confirms that late 20th-century warmth is unprecedented at hemispheric and likely global scales. There is more tentative evidence that certain climate variability modes, such as the El Niño/Southern Oscillation and the North Atlantic Oscillation, may have exhibited late 20th-century behavior that is anomalous in a long-term context. Regional conclusions, particularly for the Southern Hemisphere and parts of the tropics where high-resolution proxy data are sparse, are more circumspect. The paper highlights the limited utility of terms like the "Little Ice Age" and "Medieval Warm Period" for describing past climate epochs. Comparison of empirical evidence with proxy-based reconstructions shows that natural factors explain relatively well the major surface temperature changes of the past millennium through the 19th century, while anthropogenic forcing can explain the recent anomalous warming in the late 20th century.