This is a clear and comprehensive introduction to the topics of crystallography and diffraction for undergraduate and beginning graduate students and lecturers in physics, chemistry, materials, and earth sciences. It shows how crystal structures may be built up from simple ideas of atomic packing and co-ordination, and develops the concepts of crystal symmetry, point and space groups by way of two-dimensional examples of patterns and tilings. The concept of the reciprocal lattice is explained in simple terms and its importance in an understanding o light, x-ray and electron diffraction. Finally, the book covers practical examples of the applications of these techniques and describes the importance of diffraction in the performance of optical instruments.