1.Properties of X-RAYS. 2.The geometry of crystals. 3.Diffraction I: The directions of diffracted beams. 4.Diffraction II: The intensities of diffracted beams. 5.Laue photographs. 6.Power photographs. 7.Diffractometer measurements. 8.Orientations of single crystals. 9.The structure of polycrystalline aggregates. 10.The determination of crystal structure. 11.Precise parameter measurements. 12.Phase-Diagram determination. 13.Order-Disorder transformation. 14.Chemical-Analysis by Diffraction. 15. Chemical-Analysis by fluorescence. 16.Chemical Analysis by absorption. 17.Stress measurement. 18.Suggestions for further study.