Putting into practice the humanitarian principle of impartiality – that assistance should be given on the basis of (and in proportion to) need alone – demands both an understanding of what constitutes ‘need’ and a way of measuring it with reasonable consistency. This paper documents the findings of a year-long study into the link between needs assessment and decision-making in the humanitarian sector, which forms part of wider research commissioned by the Montreux group of donors, looking at the current system of international humanitarian financing.