According to many we are nearing a ‘golden age’ of observational cosmology with stage-IV optical telescopes such as Euclid and the Large Synoptic Survey Telescope (LSST) promising unprecedented depths and quality of data. Further cause for excitement can be provided from the upcoming Square Kilometre Array (SKA) promising to be the first 1 billion galaxy spectroscopic survey. Using radio telescopes for galaxy redshift surveys is only just beginning to become competitive and therefore now is the perfect time to be looking at ways cosmology can benefit from optical and radio synergies. In particular I will show how the use of techniques unique to radio cosmology such as 21cm intensity mapping can maximise what we learn from these future experiments.