Galaxies and clusters around and in front of radio sources

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Some recent work on radio source fields at z 0.7 and z 4 is discussed. At z 0.7 we find that radio-loud quasars are typically found in moderately rich environments independent of radio luminosity, consistent with previous results at z 0.5. In the field of the z=4.41 radio galaxy 6C0140+326 we find several candidate z>4 galaxies using the Lyman-break technique, two of which have detectable UV absorption features. In two z>4 radio galaxies, we find evidence for gravitational lensing affecting the fluxes by a few tens of percent, although we cannot rule out unusual lensing events which have larger magnifications associated with them. A simple calculation suggests lensing of z>4 radio sources should be very common.