Guidelines for the conditioning of French radioactive waste that is not acceptable for disposal in surface facilities, mainly because of their high content of long-lived isotopes, are currently being established. These wastes are produced either in liquid or solid form. They are kept safely in interim storage facilities - often on the industrial site where they were produced – by use of a whole combination of active and passive safety measures. Conditioning the waste may be envisaged in order to minimize difficulties in designing and operating storage and disposal facilities that are due to receive them now and in the future. In this regard, the physical transformations of the waste required by the production of the nuclear waste package have to be designed with a view to achieving a high level of intrinsic safety of the package, therefore facilitating the risk management of all the operations required before its final disposal. As for the favorable properties of the nuclear waste packages likely to grant them acceptance in both storage and disposal facilities, conditioning the waste aims at designing a primary confinement barrier that is able to be effective in various conditions of environment, to reduce the need for active safety measures and to provide safety margin in case of loss of one or several safety functions of the facilities. The various favorable properties of nuclear waste packages in storage and disposal facilities are discussed with focus on: - chemical reactivity of the waste, - gas release, - confinement properties, - mechanical properties, - criticality, - thermal power, - reversibility of the conditioning of the waste. As far as disposal is concerned, the difference between operation and post-closure periods is addressed.