The Lx-z distribution of the extended BCS (Ebeling et al. 1998, 2000) at z < 0.3 (blue circles) and of the MACS sample (124 clusters) at z > 0.3 (red symbols). Also plotted (open green circles) are the loci of the 23 EMSS clusters at 0.3 < z < 0.6 (Henry et al. 1992), as well as the clusters from two serendipitous ROSAT/PSPC surveys, WARPS and the 400 sq.deg. survey. The solid line marks the flux limits of the BCS and MACS surveys. By design MACS finds the high-redshift counterparts of the most X-ray luminous (and best studied) clusters in the local universe (reproduced from Ebeling et al. 2010).