This chapter describes disturbance regimes in the Intermountain Adaptation Partnership (IAP) region, and potential shifts in these regimes as a consequence of observed and projected climate change. The term "disturbance regime" describes the general temporal and spatial characteristics of a disturbance agent (e.g., insects, disease, fire, weather, human activity, invasive species) and the effects of that agent on the landscape (tables 8.1, 8.2). More specifically, a disturbance regime is the cumulative effect of multiple disturbance events over space and time (Keane 2013). The shifting mosaic of diverse ecological patterns and structures, in turn, affects future patterns of disturbance, in a reciprocal, linked relationship that shapes the fundamental character of landscapes and ecosystems. Disturbance creates and maintains biodiversity in the form of shifting, heterogeneous mosaics of diverse communities and habitats across a landscape (McKinney and Lockwood 1999), and biodiversity is generally highest when disturbance is neither too rare nor too frequent on the landscape (Grime 1973).