Based on daily surface air temperature at 2 m and 500-hPa geopotential height fields from the NCEP/NCAR reanalysis dataset, a heat wave index over Europe is calculated in this paper. Spatial characteristics of heat waves over Europe and associated atmospheric circulations are investigated using the K-mean clustering analysis method. It is shown that the heat waves over Europe can be classified into six types with different spatial patterns: Western Europe (WE), Russian (RU), Eastern Europe (EE), Scandinavian (SC), North Sea (NS), and Iberian (IB). The frequency of heatwave events over Europe is found to have increased significantly after the 1980s, which may be associated with the global warming. The decadal variability of the summer North Atlantic oscillation (SNAO) is possibly a reason for the decadal variability of European heatwaves. While the global warming can increase the frequency of European heat waves, the atmospheric internal processes that affect the strength, position, and frequency of European heat waves seem to be dominant. Composite of geopotential height anomalies shows that the occurrence region of European heat waves is determined by the position of the blocking anticyclone over Europe that is tightly tied to positive stationary wave train anomalies over Euro-Atlantic region and the phase of NAO. Low latitude-type heat waves are more likely to take place when the SNAO index decreases to a negative value, while the high latitude-type heat waves often occur during the period when the NAO index is in a positive phase. Moreover, it is found that the NAO event precedes the European blocking by 1-5 days, suggesting that the phase of NAO can modulate the European heat waves.