This paper describes a light-weight, content-based, functional query language. The Mathematical Services Query Language (MSQL) is specifically designed and implemented for querying mathematical web services described in the Mathematical Services Description Language (MSDL) and published in the MathBroker registry. Based on the client request, MSQL uses the registry querying functionality to retrieve a candidate collection of documents and then uses its own querying functionality to further filter these documents based on their contents.