This paper presents the results of research into the rippability of rock by bulldozers carried out at the University of New South Wales. A database of detailed ripping and geological data gathered from highway and mine sites in New South Wales, Australia, has been used to determine the influence of different factors on the ripping productivity of bulldozers. The dominant factors affecting productivity have been found to be the unconfined compressive strength of the rock, the degree of weathering, seismic velocity, joint roughness and strength and the spacing of joints and bedding in the unripped rock, and bulldozer mass. The database has also been used to assess several commonly used rippability prediction methods. These are shown to be generally poor predictors of both ripping productivity and difficult ripping conditions. The forces involved in ripping have been measured in the laboratory on a quarter scale model of a tine, and in the field on an instrumented full scale tine, and the relationship between force and unconfined compressive strength and depth of penetration of the tine determined. Using this information, and a multiple variable regression analysis of the database, a method has been proposed for estimating productivity and for identifying difficult ripping conditions. This paper presents the method used to gather information for the database, the results of analysis of the database to assess the influence of individual factors on ripping productivity, a review of the available methods for predicting rippability, the results of multiple variable regression analysis, and the proposed prediction method.