  Multi-object spectroscopy has been a key technique contributing to the
current era of 'precision cosmology'. From the first exploratory surveys of the
large-scale structure and evolution of the universe to the current generation
of superbly detailed maps spanning a wide range of redshifts, multi-object
spectroscopy has been a fundamentally important tool for mapping the rich
structure of the cosmic web and extracting cosmological information of
increasing variety and precision. This will continue to be true for the
foreseeable future, as we seek to map the evolving geometry and structure of
the universe over the full extent of cosmic history in order to obtain the most
precise and comprehensive measurements of cosmological parameters. Here I
briefly summarize the contributions that multi-object spectroscopy has made to
cosmology so far, then review the major surveys and instruments currently in
play and their prospects for pushing back the cosmological frontier. Finally, I
examine some of the next generation of instruments and surveys to explore how
the field will develop in coming years, with a particular focus on specialised
multi-object spectrographs for cosmology and the capabilities of multi-object
spectrographs on the new generation of extremely large telescopes.
