The class of long GRBs (LGRBs) offers some unique advantages as cosmological probes: (a) GRBs are extremely bright at all redshift and their afterglow brightness is only marginally decreasing with redshift; (b) LGRBs are associated with star formation and can thus signal and trace star formation to the highest redshift; (c) the GRB afterglow emission fades quite rapidly, allowing the study of LGRB host galaxies, forming a population of star-forming galaxies not luminosity selected; (d) GRBs provide the unique opportunity to investigate systematically both the gas in the interstellar medium from the absorption lines seen in the afterglow spectra and the ionized gas probed by the emission lines of the host galaxy spectra. In this seminar I will review the use of LGRBs as cosmological probes, showing some recent results and discussing about the impact that future space missions could have on this research field.