Dust and gas in radio galaxies and their surrounding proto-clusters

High redshift radio galaxies are among the most massive objects known out to z=5.2. I will first talk about our search for the most distant radio galaxies. Next, I will give an overview of our efforts to detect CO emission from z>3 radio galaxies using the IRAM Plateau de Bure Interferometer, resulting in 3 new detections. Finally, I will present multi-wavelength observations of the proto-cluster surrounding the z=4.1 radio galaxy TN J1338-1942. Using MAMBO at the IRAM 30m telescope, we have detected an overdensity of mm sources in this field, which may represent a population of star-forming companions within the same structure.