Abstract: Global warming has greatly intensified interactions between energy and water cycles in the climate system. Changes in the water balance increase the occurrence of regional floods and droughts. As a key component of energy-water interactions, surface evapotranspiration (ET) is important for understanding climate change. This paper focuses on the spatiotemporal variation of ET across global arid and semi-arid regions, especially its regional differences, using observations (FLUXNET-MTE) and reanalysis (ERA-Interim) dataset during 1982-2011. The results show that:(1) Mean annual ET is less than 300 mm across arid and semi-arid regions. Seasonally, minimum ET appears in winter, while maximum ET and the largest variability both appear in summer. A decadal negative-to-positive happened in the 1990s, which is particularly obvious in warm seasons. (2) At hemispheric scale, the ET variation shows a positive trend in the Eastern Hemisphere, whereas an opposite trend occurs in the western hemisphere in the last 30 years. Regarding those typical regions, ET in South Africa significantly increases by 25.14 mm (10 a)⁻¹, while that in the Southwest U.S. significantly decreases by 19.86 mm (10 a)⁻¹ (both at the confidence level of 99%). Moreover, ET slightly increases in Sahel, northern China and Australia, but slightly decreases in southern Argentina and Chile. (3) The ET variability is coupled with variations of temperature and precipitation with a similar annual cycle. However, the spatial patterns of correlation between ET and temperature/precipitation are heterogeneous across the arid and semi-arid regions.