Thanks to the development of metallographic and optical techniques, the quantitative characterisation of the geometry of rough surfaces has become very useful in practical applications. Today, numerous different methods are available for determining three dimensional co- ordinates, linear profiles or height contours to a reasonable degree of accuracy and within an acceptable time frame, and for evaluating such data. In this article, the use of such techniques in the field of fractography is demonstrated with reference to a number of case studies dealt with by the author s own team, supplemented by several examples from other research groups. The following examples are discussed:In a ceramic material different fracture paths were discerned corresponding to different test temperatures.Inhard metals,it was shown that hoth the sub-critical and supercritical propagation of cracks occurred dalong the same path.From measurements of the proportion of fracture surfaces occurring along and in the various different phases present and the depth of dimples occurring during ductile fracture in the binder phase,the fracture energy of EC-Co-hard alloys with different cobalt contents and tungsten carbide grain sizes was calculated and found to be in excellent agreement with actual experimental results.In the case of ceramic fibre-aluminium matrix cpmposite materials,by measuring the beight distribution of the positions of fracture of the fibres,the load transfer in the region of the fracture surface was determined.with this information a model was developed which explains the significant variation in strength of these materials Finally,a model was developed for metallic materials using which,from the experimentally determined distributions of the height and inclination of the fracture facets,the stress intensity of roughness induced crack closing could he accurately predicted.