This part of ISO 23900 provides an introduction to the various parts of ISO 23900 which describe methods for dispersing pigments and extenders in plastics materials in order to determine their dispersion characteristics and colouristic properties. Methods of assessing dispersion characteristics are described in the subsequent parts of ISO 23900. The various procedures described permit comparison to be made between similar pigments (for example between a test sample and an agreed reference pigment). The results provide an indication of relative dispersibility under practical conditions of use, provided that the test procedure and plastics material selected are appropriate.