This course aims to relate properties and structure, and to provide a theoretical basis upon which to extrapolate when conditions or materials outside previous experience arise. The present text refers primarily to metals and alloys, other (non-crystalline) solids are treated rather less fully. This course is largely dictated by the state of knowledge at the present time, for although there is a large mass of data concerning the properties of non-metallic materials, much of this is empirical and a full explanation is made difficult by the complexities of an irregular initial structure. The course covers constitution, properties, and significance of test data. Separate lectures discuss properties such as heterogeneity, elasticity, plasticity, fracture, and mechanical testing methods, such as tensile and hardness tests; creep, fatigue and impact tests. Throughout the course, the instructor will confine the discussion to those aspects of materials science which appears to be reasonably well understood at the present time.