Since the 1980s international development activities have increasingly been transferred from government organisations to International Non Government Organisations (INGOs). In this article we argue that the trend for NGOs to increasingly undertake government-funded tasks leads to conflicts between the different sources on which the legitimacy of the NGO is based. In particular considerable friction may exist between output and normative legitimacy. Output legitimacy relates to the degree to which an organisation is able to achieve specified results. These results are supposed to coincide with specific performance indicators stipulated in project proposals. Normative legitimacy is based on values (as stated in the vision or mission of the organisation) on which the organisation is founded. We find that INGOs have an incentive to emphasise output legitimacy over normative legitimacy. Secondly, we argue that in response to this friction, NGOs are driven to actively 'create' legitimacy by organisation presenting projects as being 'successful'. Thirdly, we contend that this friction may also affect the approach developed by INGOs for specific projects. This approach will focus on those activities, target beneficiaries and select areas, which are seen as offering the greatest potential for a successful project. These arguments are developed by focusing on two water services projects undertaken by an international NGO in Lilongwe, Malawi and in Maputo, Mozambique. Fieldwork for developing the two case studies was undertaken from November 2008 to February 2009 (Lilongwe) and June 2009 to November 2009 (Maputo).