Formal approaches to software specification and development have been a topic of active research for a long time. There now exists an important corpus of knowledge and results in this domain. There is more and more interest in the industrial applications of these techniques, even if it is generally observed that transfer is difficult in this area. The article surveys formal specification techniques, but, as it is difficult (and probably meaningless) to speak of such techniques independently from the development process, some formal development methods are discussed, as well as the impact of formal specifications on the development activities. >