The complexities of the internal friction and dynamic modulus of metals in the cold‐worked condition may be understood reasonably well by separation of the phenomena into the following three distinct effects: (1) the ``nonlinear'' effect, characterized by strong amplitude dependence, frequency independence, and its disappearance after severe deformation; (2) the Ko¨ster effect, which shows rapid recovery after deformation, at temperatures well below the recrystallization temperature; (3) the ``viscosity'' effect, characterized by strong frequency and temperature dependence. The origin of each of these effects is briefly discussed from the point of view of dislocation theory.