The strength of particles depends on a variety of factors such as their material and mechanical properties, their size, shape, the loading pattern and other external conditions. This paper considers the breakage phenomena in particles and granules with an emphasis on the history of loading and the material properties. According to the mechanical response and the type of failure, particles are classified as brittle, semi-brittle, and ductile. The strength of brittle and semi-brittle, homogeneous and heterogeneous spherical particles is discussed. Experimental data on sodium benzoate granules and microcrystalline cellulose particles, which was obtained in a new robotic compression tester, is employed to illustrate and discuss the concepts of strength. (C) 2004 Published by Elsevier B.V.