The Medieval Warm Period (MWP) or Medieval Climate Optimum is a time of warm climate in the North Atlantic region, that may also have been related to other climate events around the world during that time, including in China, New Zealand, and other countries lasting from about CE 950–1250.

It is followed by a cooler period in the North Atlantic termed the Little Ice Age.

Some refer to the event as the Medieval Climatic Anomaly as this term emphasizes that effects other than temperature were important.

Despite substantial uncertainties, especially for the period prior to 1600 when data are scarce, the warmest period prior to the 20th century very likely occurred between 950 and 1100, but temperatures were probably between 0.1°C and 0.2°C below the 1961 to 1990 mean and significantly below the level shown by instrumental data after 1980.

The heterogeneous nature of climate during the ‘Medieval Warm Period’ is illustrated by the wide spread of values exhibited by the individual records.