Linguistic research and language technology development employ large repositories of ordered trees. XML, a standard ordered tree model, and XPath, its associated language, are natural choices for storing and querying linguistic data. However, several important expressive features required for linguistic queries are missing in XPath. In this paper, we motivate and illustrate these features with a variety of linguistic queries. Then we define extensions to XPath which support linguistic tree queries. We provide a relational representation for trees, and define an SQL translation for queries. Experiments demonstrate that the query system is significantly faster than other linguistic tree query systems for a wide range of queries. 1