In the last few years there has been an increasing interest in studying ontology evolution and versioning for the World Wide Web, in particular, applied to OWL. However, little attention has been given to the problem of Web services evolution, with a focus on OWL-S, an ontology of services recently proposed. In this paper, we show that recent work on Temporal RDF can be extended to support versioning of an ontology of services. We introduce a formal model and a query language that allow accessing different versions of an OWL-S specification. We present the language semantics and discuss complexity issues. We show how our proposal can be implemented within the OWL-S framework.