Because of their role both as rain producers in tropical regions and as starting points of many tropical cyclones, understanding easterly waves is a very important problem in tropical meteorology. We take advantage of the new reanalysis data sets provided by NCEP/NCAR to verify previous findings and make more detailed studies about the general characteristics of easterly waves. We study the 2-8 day synoptic scale disturbances during the Northern Hemisphere summer using four times daily NCEP/NCAR global gridded reanalysis data for the 1968-1997 thirty year period. We analyze the global distribution of the disturbances, their three dimensional structure, propagation characteristics and low frequency variabilities using methods such as lag correlation techniques, empirical orthogonal functions and spectral analysis