Abstract : Web services offer a number of valuable features towards supporting the development of open distributed systems, built out of the composition of autonomous services. Nonetheless, the resulting systems must offer a number of non-functional properties and in particular dependability-related ones, for acceptance by users, including effective exploitation in the e-business domain. This thesis proposes a method and associated middleware services for the dependable composition of autonomous systems. Our contribution subdivides into the extension of the interfaces of systems with their dependability capabilities, a definition of a specific composition language oriented towards providing dependability for the composite system and a runtime support that implements fault tolerance mechanisms. The proposed extension of Web service interfaces is specified using a conversation language that sets the rules for calling the operations offered by individual Web services. Recovery-related properties are associated to these conversations, enabling to reason about the recovery strategy that can be implemented in the service composition. Indeed, the recovery behaviour of composite services depend upon the recovery properties of the composed Web services, since the latter must ultimately perform some recovery actions in the presence of faults. This thesis further proposes a declarative composition language, which allows developing composite Web services in terms of dependable actions. We allow exception handling involving several Web services to be specified at the composition level, enabling in particular to integrate non-dependable Web services in the composition while still supporting dependability of the composite service. We show that fault tolerance can be obtained as an emergent property of the aggregation of different, potentially non-dependable, services.