The paper discusses the extent and nature of the internal changes in a metal subjected at a suitable temperature to a steady stress sufficiently high to produce flow and rupture. The general strength of metals at high temperatures is compared with that of other metals at atmospheric temperatures. Flow occurs in metallic aggregates by three means which are not necessarily independent, namely, by slip within the crystals, by grain boundary movement, and by continuous recrystallization under stress. The method of ascertaining the rate of creep and estimating significance of the tests are briefly described in relation to the probable mode of flow. The connection between the flow and the previous condition of the metal,i. e., whether cast or worked, etc., is related to the microstructure and grain size. Further factors, such as the action of grain boundary and crystalline material, within the grains are discussed in relation to their effect on intercrystalline rupture and slip. Evidence is given of the importance of these factors by the consideration of a case of an alloy which age‐hardens on exposure to service temperatures. Further factors, such as the effect of temperature, are referred to in the concluding portion of the paper.