This paper deals with the properties of dislocations in some ceramic materials. The implication of the intimate structure of dislocations revealed at the TEM level, on the macroscopic properties is discussed. Not only consequences on mechanical properties are taken into account but also consequences on physical properties. Examples are given for structural ceramics (ZrO2), as well as for superconducting ceramics (YBa2Cu3O7-∞). In this latter class of materials it is shown that dislocations can be used to locally change the thermodynamic range of nucleation of non stoichiometric phases. Pinning of vortices by dislocations is also discussed.