During the past thirty years various accelerogram data sets recorded by “free field” strong-motion stations in Greece have been compiled by two institutes that are in charge of running national strong-motion networks. These data sets have been of limited potential use for research because of nonstandard processing, nonhomogeneous earthquake parameters adopted, and a minimum standard of site characterization based only on surface geology. In addition, given an ever-increasing cumulative number of accelerograms, a database was required to facilitate data selection by users. To satisfy all these issues we have developed HEAD version 1.0—a unified HEllenic Accelerogram Database—which is briefly presented in the present paper. Homogeneous strong-motion data processing and site characterization based on detailed borehole data or/and Vs profiles allow the data to be used to their full potential. Instrument and housing characteristics are provided for each station, and relocated earthquake hypocenter parameters and moment-magnitude are given for each earthquake. Understanding the nature of strong ground motion is of crucial importance in reducing seismic risk worldwide. Publication of strong-motion data is essential for development of building codes and design methods for large engineering structures as well as for development of near-field seismology. After realizing the need for organized strong-motion data sets, the scientific community has developed user-friendly databases (among others, Kinoshita, 1998; Steidl and Lee, 2000; Ambraseys et al. , 2002; LDEO/NCEER, 2003). In Greece, deployment of a strong-motion network began in the early 1970's under the auspices of the Geodynamic Institute (GEIN) of the National Observatory of Athens; ten years later the Institute of Engineering Seismology and Earthquake Engineering (ITSAK) began an effort to install a new strong-motion network throughout Greece. Prior to 2000 the vast majority of strong-motion instruments of the national network were analog (SMA-1 Kinemetrics). In recent years, analog recorders have begun to …