The XMM Cluster Survey (XCS) is a serendipitous search for galaxy clusters using all publicly available data in the XMM-Newton Science Archive. Its main aims are to measure cosmological parameters and trace the evolution of X-ray scaling relations. In their paper, the authors present the first data release from the XMM Cluster Survey (XCS-DR1). This consists of 503 optically confirmed, serendipitously detected, X-ray clusters. Of these clusters, 256 are new to the literature and 357 are new X-ray discoveries. They present 463 clusters with a redshift estimate (0.06 < z < 1.46), including 261 clusters with spectroscopic redshifts. The remainder have photometric redshifts. In addition, the authors have measured X-ray temperatures (kT<sub>X</sub>) for 401 clusters (0.4 < kT<sub>X</sub> < 14.7 keV). This table was created by the HEASARC in May 2013 based on <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/MNRAS/423/1024">CDS Catalog J/MNRAS/423/1024</a> file xcsdr1.dat. This is a service provided by NASA HEASARC .