  We present the statistically complete and cosmologically most relevant subset
of the twelve most distant galaxy clusters detected at z>0.5 by the MAssive
Cluster Survey (MACS). Ten of these systems are new discoveries; only two
(MACSJ0018.5+1626 aka CL0016+1609, and MACSJ0454.1-0300 aka MS0451.6-0305) were
previously known. We provide fundamental cluster properties derived from our
optical and X-ray follow-up observations as well as the selection function in
tabulated form to facilitate cosmological studies using this sample.

Astrophysics