This paper, produced for the Wilton Park conference on "Enhancing the effectiveness of  parliaments: Challenges and opportunities", 27-30th October 2008, summarises a research project which aimed to generate better evidence about parliamentary strengthening, in order to inform decisions about whether and how to provide support to parliaments in developing countries. The project – a collaboration between ODI and the Parliamentary Centre, with funding provided by DFID and CIDA – has involved four country case studies; Cambodia, Ghana, Tanzania and Uganda. The vantage point taken for our analysis is that of the Paris Principles on Aid Effectiveness.