The improved resolution of the Viking orbiter images has led to the discovery of a number of unusual features on the surface of Phobos: (1) elongated rill-like depressions associated with the crater Stickney (possibly surface fractures), (2) chains of irregular craters which sometimes show a 'herringbone' pattern (possibly secondaries), and (3) sets of almost parallel linear striations of uncertain origin. The crater chains are not randomly oriented but tend to lie parallel to the orbital plane of Phobos. The striations, on the other hand, appear to form arcs of small circles which are normal to the Mars-Phobos direction. With the possible exception of feature (2), similar features have not been recognized on Deimos, possibly because of the coarser resolution of available imagery. The Viking data demonstrate that the surfaces of both satellites are definitely saturated with craters ?300 m across.