This paper provides a review of different particle size scales, size class terminology and particle size distribution (‘textural’) classification schemes which are widely used in sedimentology, geomorphology, soil science, aquatic ecology and civil engineering. It is concluded that a revised system of size class nomenclature, based on theUdden (1898) and Wentworth (1922)schemes, provides the most logical and consistent framework for use with sediments and a wide range of other particulate materials. A refined scheme is proposed which has five first-order size classes (boulder, gravel, sand, silt and clay), each of which has five second-order subdivisions with limits defined at one phi intervals. The scheme is simple and intuitively easy to understand. The paper also provides a review of previous schemes that have been proposed to describe and classify sediments on the basis of the proportions of gravel, sand and mud, or sand, silt and clay using trigons (also termed ternary diagrams). Many of these schemes do not have a logical basis and provide limited or uneven resolution. New gravel, sand and mud and sand, silt and clay classification systems are proposed that are both more logical and provide greater discriminatory power than previous schemes; they are therefore more suitable for use in environmental and forensic investigations. A new Microsoft Excel® program, freely available to download fromhttp://www.kpal.co.uk, allows rapid classification of sediments based on the proportions of gravel, sand and mud and sand, silt and clay proportions and graphical comparison of the data for different sample groups.