MOS: A critical tool for current and future radio surveys

Since radio continuum observations are not affected by dust obscuration, they are of immense potential diagnostic power as cosmological probes and for studying galaxy formation and evolution out to high redshifts. However, the power-law nature of radio frequency spectra ensures that ancillary spectroscopic information remains critical for studying the properties of the faint radio sources being detected in rapidly-increasing numbers on the pathway to the Square Kilometre Array. In this contribution, I present some of the key scientific motivations for exploiting the immense synergies between radio continuum observations and multi-object spectroscopic surveys. I review some of the ongoing efforts to obtain the spectra necessary to harness the huge numbers of star-forming galaxies and AGN that current and future radio surveys will detect. I also touch on the WEAVE-LOFAR survey, which will use the WEAVE spectrograph currently being built for the William Herschel Telescope to target hundreds of thousands of low frequency sources selected from the LOFAR continuum surveys.