The redshift regime 1<z<2 corresponds to the epoch during which the first massive galaxy clusters assemble. It is also during this era that the present day star-formation density relation is established, with star formation rates in cluster galaxies decreasing to well below the field level. In this talk I will present results from high-redshift cluster searches with the Spitzer and WISE telescopes, which are helping to open up this redshift window for detailed studies of the cluster galaxy population. I will show that by z=1.5 we are finally witnessing significant galaxy assembly and in situ star formation.  Additionally, I will demonstrate how these programs are pushing the extremes in redshift and mass for detection of galaxy clusters, and discuss potential cosmological implications.