Streamflow processes of 12 rivers in western Europe are investigated for trend and nonstationarity in the full 100-year period in the 20th century. Trend analyses with Mann–Kendall test show that there is no trend in annual mean discharges. Only three annual maximum flow series exhibit significant trends (Rhine and Moselle, upward; Rhone, downward). There are two minimum flow series exhibiting significant downward trend (Maas and Thames) and five exhibiting upward trend (Danube, Elbe, Weser, Reuss and Rhone). Monthly flow series are examined with seasonal Kendall test. A significant downward trend is observed in the monthly flow series of Maas, whereas a significant upward trend is observed in the monthly flow series of Rhone. Meanwhile, significant heterogeneity in trends among different months is observed in three Alpine rivers (Inn, Reuss and Rhone). ADF and KPSS tests which originate from econometrics are introduced to test for nonstationarity in streamflow series at three characteristic timescales. All annual mean discharge series and most monthly mean discharge series appear to be stationary. But only 2 out of the 12 daily series are statistically stationary.