  Clusters of galaxies need to be investigated using complementary approaches
combining all currently available observational techniques (X-ray,
gravitational lensing, dynamics, SZ) on homogeneous samples if one wants to
understand their evolution and physical properties. This is particularly
important in order to relate the observable quantities to the cosmologically
important cluster mass. We present here a number of on-going projects that aim
at studying cluster physics for samples based on currently available all-sky
X-ray surveys such as XBACs, BCS and MACS.
