I will briefly review the technique of intensity mapping, an emerging technique for probing large-scale structure and dark energy via Baryon Acoustic Oscillations (BAOs). I will discuss a new single-dish experiment, BAOs In Neutral Gas Observations (BINGO), which will map redshifted HI across 2000 sq. deg. at a sensitivity of ~100 microK. BINGO aims to detect BAOs at z=0.1-0.5 thus allowing constraints on the expansion history of the Universe and dark energy. Although simple in concept, I will discuss the major challenges for this experiment, including horn fabrication, foreground removal and calibration (and obtaining funding!). I will also discuss prospects for intensity mapping with the SKA.