The variability and trend in global precipitable water vapor (PWV) from 1979 to 2014 are analyzed using the PWV data sets from the ERA-Interim reanalysis of the European Centre for Medium-Range Weather Forecasts (ECMWF), reanalysis of the National Centers for Environmental Prediction (NCEP), radiosonde, Global Positioning System (GPS), and microwave satellite observations. PWV data from the ECMWF and NCEP have been evaluated by radiosonde, GPS, and microwave satellite observations, showing that ECMWF has higher accuracy than NCEP. Over the oceans, ECMWF has a much better agreement with the microwave satellite than NCEP. An upward trend in the global PWV is evident in all the five PWV data sets over three study periods: 1979-2014, 1992-2014, and 2000-2014. Positive global PWV trends, defined as percentage normalized by annual average, of 0.61 plus or minus 0.33%decade super(-1), 0.57 plus or minus 0.28%decade super(-1), and 0.17 plus or minus 0.35%decade super(-1), have been derived from the NCEP, radiosonde, and ECMWF, respectively, for the period 1979-2014. It is found that ECMWF overestimates the PWV over the ocean prior to 1992. Thus, two more periods, 1992-2014 and 2000-2014, are studied. Increasing PWV trends are observed from all the five data sets in the two periods: 1992-2014 and 2000-2014. The linear relationship between PWV and surface temperature is positive over most oceans and the polar region. Steep positive/negative regression slopes are generally found in regions where large regional moisture flux divergence/convergence occurs. Key Points * ECMWF PWV shows a better performance than NCEP one as evaluated by radiosonde, GPS, and microwave satellite * Upward global PWV trends are observed from five types of data sets in the period of 1979-2014 and become more apparent in recent years * Positive PWV-temperature regression slopes are observed over most oceans, and negative values are found over many continents