FOR the third year in succession, members of the Department of Mineralogy and Petrology and the Cavendish Laboratory at Cambridge were able, through the courtesy of Prof. C. E. Tilley and Sir Lawrence Bragg, to conduct a summer school in X-ray crystallography; the administration was under the control of the Board of Extra-Mural Studies. The first part of the course, which was attended by everyone, dealt with crystal symmetry and the use of stereographic and gnomonic projections. Then followed fundamental theory and practice in the interpretation of the various types of X-ray photographs, the production and properties of X-rays and the measurement of intensities of X-ray reflexions. The methods of taking, interpreting and using powder photographs were dealt with in some detail. The school differed from those previously held in that during the last two days it was divided into two groups (as it happened, into almost equal numbers), one of which studied further theory and practice in the elucidation of fundamental crystal structure, such as the theory of space groups, structure factors, use of absent spectra to determine space groups and parameter determination; the second group studied powder photographs in relation to metallurgical problems such as the determination of grain size, stress and the orientation of crystals in drawn wires and rolled sheets. Throughout the course the labour of computation was greatly reduced by the use of graphical methods and the provision of tables in which many of the factors in formulae had already been worked out. Of the thirty-one who attended the course, eight were from universities, two from research institutes, one from a technical college, two from research associations, three from Government laboratories and fifteen from industry. The opportunity for interchange of ideas afforded (especially at tea served in the laboratory after the day's work) was one of the most valuable aspects of the course. The success of these schools at Cambridge should encourage other authorities to develop this aspect of university education.