Abstract : Software engineering must cope with a more and more increasing need for evolutivity of software systems in order to make their maintenance and more generally their administration easier. However, evolution and especially dynamic evolution in a system must not be done at the expense of its reliability, that is to say its ability to deliver the expected functionalities. Actually modifications in a given system may let it in an inconsistent state and so it can have an impact on its reliability. The aim of this thesis is to guarantee reliability of dynamic reconfigurations used to make systems evolve at runtime while preserving their availibility, i.e. their continuity of service. We are especially interested in component based and distributed systems. The system architecture can be used as a support for dynamic, non-anticipated (also called ad-hoc) and concurrent reconfigurations. We propose a definition of consistency for configurations and reconfigurations in the Fractal component model with a model based on integrity constraints like for example structural invariants. Reliability of reconfigurations is ensured thanks to a transactional approach which allows both to deal with error recovery and to manage reconfiguration concurrency in systems. Finally, we propose a modular component-based architecture so as to implement transactional mechanisms adapted to dynamic reconfigurations in Fractal applications.