GNOSIS is an OH suppression unit to be used in conjunction with existing spectrographs. The OH suppression is achieved using fibre Bragg gratings (FBGs), and will deliver the darkest near-infrared background of any ground-based instrument. Laboratory and on-sky tests demonstrate that FBGs can suppress OH lines by 30dB whilst maintaing > 90% throughput between the lines, resulting in a ≈ 4 mag decrease in the background. In the first implementation GNOSIS will feed IRIS2 on the AAT. It will consist of a seven element lenslet array, covering ≈ 1.4″ on the sky, and will suppress the 103 brightest OH lines between 1.47 and 1.70 μm. Future upgrades will include J-band suppression and implementation on an 8m telescope.