These guidelines describe methods for the evaluation of treatment services and systems for substance use disorders. The guides are intended to be a companion resource to the WHO/UNDCP/EMCDDA workbook series on the evaluation of costs and effects of treatment for substance use disorders. The main audience is policy makers, commisioners of treatment services and treatment agency personnel who want to know more about research evaluation and commission or undertake evaluation studies. The guidelines are intended to be of particular interest for countries where research and evaluation in this area is not widely developed. The aim here is to offer a concise description of the main evaluation methods and to encourage users to adopt evaluation methods to help develop and maintain effective and efficient treatment servies and treatment systems.