This guide has been compiled in response to a generally expressed desire on the pa rt of both users and manufacturers for guidance on the use of quartz crystal filters so that the crystal filters may be used to their best advantage. It is not the aim of this guide to explain theory, nor to attempt to cover all the eventualities which may arise in practical circumstances. The guide draws attention to some of the more fundamental questions which should be considered by the user before placing an order for a crystal filter for a new application. It is of prime interest to a user that the filter characteristics should satisfy a particular specification, while the resonators to meet the specification should be at the discretion of the manufacturer.