This chapter shows how to create a parser for a query language. A query language parser translates textual queries into calls to an engine. Commercial databases send queries to an engine that comes with the database product. Instead of using a commercial engine, this chapter uses the logic engine developed in Chapter 12. The engine proves the query against a data source and returns successful proofs as the result of the query. For its examples this chapter uses Jaql, a query language created for this book.