Query answering has been addressed as a key issue in dynamic distributed environments. An important step in this process is reformulating a query posed at a peer into a new query expressed in terms of a target peer, considering existing correspondences between them. In this book, we present a semantic-based approach, named SemRef, which brings together both query enrichment and query reformulation techniques in order to provide users with a set of expanded answers. To this end, we make use of semantics which is mainly acquired from a set of semantic correspondences that extend the ones commonly found. Furthermore, we take into account the context of the user, of the query and of the environment as a way to enhance the overall process and to deal with information that can only be acquired on the fly.