Spectroscopic and Tomographic observations of galaxies in the first Gyr: now and in the future

I will present the latest results on the typical spectroscopic properties of galaxies in the early Universe from various JWST emission-line surveys. I will show how we used JWST/NIRCam grism data to confirm redshifts for ~2000 galaxies at z=3-9, and simultaneously measured their distributions of star formation rate, mass and metallicity. I will also discuss the role of galaxies in reionizing the Universe based on measurements of the cross-correlation between galaxies and Lyman-alpha transmission spikes in background quasar spectra. I will finally discuss how deep future spectroscopy with the ELT can simultaneously advance our understanding of the massive stars, galactic winds in distant galaxies, and the diffuse gas around galaxies in their foreground, illustrated with the first case study in the MUSE eXtremely Deep Field.