The debris component of the dislocation sub-structure in single crystals deformed at 78K was studied by means of weak-beam transmission electron microscopy. Primary unfaulted dipoles, faulted dipoles, stacking-fault tetrahedra and defect clusters were identified. It was shown that all of these defects could be derived from primary dislocations. The distribution of dipole sizes, as a function of flow stress, suggested that they were refined by chopping as deformation proceeded so, just before fracture, their lengths varied from 30nm down to vanishingly small loops. The size distribution of stacking-fault tetrahedra exhibited a small dependence upon the degree of deformation, and suggested that some equilibrium size for the defects was established in the presence of other elements of the sub-structure. Small (less than 2nm) dot-like clusters were suggested to be the remains of larger entities that had shrunk during warming to room temperature. Rearrangement of the structure, which occurred between 78K and room temperature, were suggested to explain large observed changes in electrical resistivity.Transmission Electron Microscopy Observations of Debris Structure in Deformed Copper Single Crystals. M.Niewczas: Philosophical Magazine A, 2002, 82[2], 393-414