Voids are the largest component by volume of the cosmic web. As large
underdense regions they serve as excellent laboratories for testing
general relativity. In this seminar I shall give an overview of the search
for and classification of voids in spectroscopic redshift surveys, in
particular VIPERS. I shall then demonstrate how studies of the cross
correlation between galaxies and voids can be used to measure the growth
rate of structure in simulations, and cover recent attempts to apply these
techniques to data.