A review is given on the effect which dislocations have on superconducting properties. A distinction is made between mean free path effects and non-equilibrium effects. Mean free path effects result in a decrease or an increase of the critical temperature depending on the relative importance of the anisotropy of the energy gap or internal stresses present in the superconductor. A second mean free path effect is the increase of the upper critical fields. Non-equilibrium effects arise by the interaction between defects and flux lines in the mixed state of a type II superconductor. The flux lines can be pinned by defects in the superconductor. The pinning properties of three types of structure are discussed : 1) a uniform dislocation distribution, 2) an inhomogeneous distribution, such as polygonization walls, or a cell structure and 3) large two dimensional inhomogeneities such as a fiber structure or grain boundaries. It is suggested that pinning becomes more effective in this sequence