Climbing of dislocations is dependent upon the variation in the number of point defects in the crystal; atomic transport cannot, in general, take place except by thermally activated means. Such a process can be described by the diffusion of jogs along the dislocation when the latter is perfect. In the case of an extended dislocation, such jogs, being more difficult to form, become too rare to explain climbing. Two mechanisms of emission or absorption of point defects by extended dislocations as a function of temperature, T, of stress, σ, and of the supersaturation of point defects, c c 0 , are proposed for this last case. One or the other cannot become active unless the values of c c 0 are high or low. The physical conditions for their operation are not greatly dependent upon the nature of the metal considered and are influenced only through the tension of the stacking fault. While the conditions given below pertain to copper, they can be adopted to other metals with changes of only a few hundredths. Climbing is easiest for the edge of a band of stacking faults formed from extended dislocations. This places a portion of the fault in the nearest neighbouring plane the limits of which form a dipole in the fault plane. The easiest to climb are probably the extended edge dislocations which emit or absorb beginning at values of U = kT ln c c 0 + σb 3 ⩾ 0.40 eV. Beginning at 0.65 eV, partial screw dislocations can become active as well as the nuclei of such dipole loops at even the interior of the fault. The second mechanism consists in the nucleation and growth of imperfect dislocation loops at the interior of the bands in which these form “holes”, i.e. regions where the tension of the stacking fault is lower or even zero. Geometrically, this is realized when a vacancy cluster in the plane of the band, for example, collapses. Energetically, such a process is not possible unless U > 0.50 eV in the rare cases of nuclei containing three or four vacancies only. Finally, these loops may serve as stable anchors at high temperatures for extended dislocations.