Abstract　 　　 

　 The standard model of cosmology, a universe dominated by cold dark matter, directly predicts that bounded systems on various scales -- galaxies, groups of galaxies, and clusters of galaxies -- evolved from a near-uniform Big Bang through hierarchical formation. Such a scenario naturally gives rise to questions such as how well can self-similarity hold for systems on different scales and what is the role played by baryon physics in their evolution. 90% of the baryons in galaxy groups and clusters are in the form of hot gas emitting in X-rays through bremsstrahlung radiation. Together, three ongoing major X-ray missions (Chandra, XMM-Newton and Suzaku), with different advantages to complement each other, enable us to study various physics and over a wide range of physical parameters. I will talk about recent studies of baryon physics in clusters and groups, such as gas fraction, gaseous clumpiness, AGN feedback, ram pressure, and metal enrichment.