Abstract
It has now been established that paracrystals are the 'building blocks' of many materials including polymers, biological materials, colloids, molten metals and alloys, and catalysts. The concept of paracrystallinity and the main equations which are needed for the practical application of the theory to X-ray, neutron and electron diffraction are presented in a simplified style which can be easily grasped by scientists from all disciplines. Examples of the application and usefulness of the theory which support the fact that paracrystals are the building blocks of condensed matter are presented. X-ray diffraction, neutron diffraction, electron diffraction, scanning electron microscopy and transmission electron microscopy are among the techniques which have been used for the assessment of the paracrystalline nature of the materials given in the examples.