Hydrogen is the most abundant element in the universe, and in its neutral phase (HI) radiates at a wavelength of 21-cm. The redshifted 21-cm line can potentially probe a significant fraction of the universe, shedding light on astrophysical processes and fundamental physics. Recently, two observational redshift windows have emerged: around the epoch of cosmic reionization (EoR), 21-cm line directly traces the distribution and evolution of neutral/ionized regions, probing the reionization history; at redshifts around unity, 21-cm follows large-scale structure and can be used to measure the Baryon Acoustic Oscillation signature, constraining the properties of dark energy. I will describe our current efforts in these two fields, utilizing the Giant Metrewave Radio Telescope (the GMRT-EoR project) and the Green Bank Telescope (GBT), aiming to measure the 21-cm power spectrum at redshifts around nine and one, respectively. Initial results are encouraging. As both experiments ! are in the 'intensity mapping' regime, I will also briefly discuss recent ideas of CO intensity mapping at redshifts around EoR, which complements the 21-cm measurements.