In this paper, we present an approach to easily define flexible and reliable services compositions. We introduce a new concept called transactional patterns to specify flexible and reliable composite Web services. A transactional pattern is a convergence concept between workflow patterns and advanced transactional models. It can be seen as a coordination pattern and as a structured transaction. Thus, it combines workflow flexibility and transactional processing reliability. Designers can simply connect together a set of transactional patterns to define a composite Web service. We use a set of techniques to ensure control and transactional coherence between patterns inside a services composition.