The ability to assess intracluster gas velocities directly is key to understanding the gas dynamics and determining the evolutionary stage of galaxy clusters. This ability was made possible only very recently, with the new generation of high spectral and spatial resolution X-ray spectrometers with good gain stability. We pioneered the technique to extract intracluster gas velocity distributions directly from X-ray spectroscopy and detected significant gas bulk velocities in several galaxy clusters. The high velocities found in clusters have an impact not only on the internal energetics of galaxy clusters and interaction with member galaxies but also indicate significant non-thermal support against gravity. This has a fundamental bearing on the derived clusters masses and baryon fraction widely used to constrain cosmological parameters.

I will discuss the current state of this search with ASCA, Chandra, XMM-Newton and Suzaku satellites, how this method compares with indirect measurements of bulk velocities and the future prospects of this study in other wavelengths and also including cosmological simulations.