For four decades, wide and deep spectroscopic surveys have been a major tool for extragalactic studies. From precursor surveys with a few hundred galaxies (such as the CFRS in the 1990s) to current projects aimed at collecting several million z>1 redshifts (such as Euclid, PFS), several generations of increasingly deep and massive spectroscopic surveys have revolutionised our understanding of the universe. They have enabled detailed studies, on statistically significant samples, of galaxy evolution processes such as star formation, mass assembly, merging and interaction with the environment in a cosmological context. Advances in instrumentation have pushed observational limits, now allowing us to probe the epoch of reionization with unprecedented large samples of objects. With the current generation of large spectroscopic surveys about to begin, we are now entering the era of precision cosmology. These surveys will profoundly improve our understanding of dark matter, dark energy and of the detailed physics of galaxies in relation to their local (circumgalactic) and large-scale intergalactic environments. Olivier Le Fèvre has pioneered, led and tirelessly promoted several of the largest spectroscopic surveys to date. He has been at the forefront of these scientific topics for decades. This conference is a tribute to his legacy.