The problem of radio interference is particularly acute when consideration is being given to ionospheric scatter communication. This is mainly brought about because of the low level of scatter signals and the consequent need for high-gain receiving aerials. A wide variety of both man-made and natural interference has been encountered in the United Kingdom during an investigation into the behaviour of scatter transmissions from Gibraltar. Furthermore, specific surveys have been made which have yielded valuable information concerning disturbances at other geographical locations. The problem resolves itself mainly into two categories: (a) disturbances which have their sources in the vicinity of the receiving aerial, and (b) disturbances which are propagated over great distances. Type (a) can be largely overcome by adequate separation of the receiving site from disturbing sources, and by careful design of the receiving aerial; type (b) could be overcome by raising the operating frequency.