Professor Alexander (Alex) Moodie has played an essential part in the theortical and experimental developments which have revolutionised the fields of electron diffraction and microscopy of crystals in recent years. His theoretical work has included important contributions to the initial formulation of a complete n-beam theory of electron diffraction, the formal quantum mechancial basis for this and the computing methods permitting its application to practical problems. He has initiated the development of several new experimental techniques and methods and has pioneered the application of these and established techniques to the confirmation of theoretical results and to problems of importance in solid-state physics and chemistry.