The Hoek-Brown failure criterion was originally developed for estimating the strengths of hard rock masses. Because of the lack of suitable alternatives,  the criterion has been applied to a variety of rock masses including very poor quality rocks, which could almost be classed as engineering soils. These applications have necessitated changes to the original criterion. One of the principal problems has been the determination of equivalent cohesive strengths and friction angles to meet the demands of software written in terms of the Mohr-Coulomb failure criterion. This paper summarises the interpretation of the Hoek-Brown failure criterion which has been found to work best in dealing with practical engineering problems.