South of the high mountain axis of the Pyrenees the southern margin, known as the Prepyrenees, forms a distinctive, rela- tively homogeneous region. This paper provides an overview of the geomorphic processes affecting the montane belt (between 800 and 1,600 m a.s.l.) of the Prepyrenees. It is based principally on detailed fieldwork in two areas undertaken by researchers of the Institute Pirenaico de Ecologfa, Jaca. An outline of the geology, climate, vegetation, and land use is provided as an essential base for discussion of the active geomorphic processes. Hillslope runoff processes include sheet and rill erosion, typical of gentle slopes where human disturb- ance has been most extensive, while gully erosion is most active in headwater areas least affected by human disturbance. Mass movements are common, especially where deep soils, high in montmorillonite, occur. Landslides, and other forms of rapid mass move- ment, respond to torrential rainstorms with long recurrence intervals. During the extreme rainfall event of November 1982, 342 mm of precipitation was recorded in 48 hours; this and its observed geomorphic effects serve as a valuable guide for landscape interpretation.