This HPG Background Paper is the first significant attempt to assess private sector humanitarian financing trends over the period 1995–2005. By ‘private sector’ we mean funding flows by private individuals, corporations and charitable foundations to international humanitarian action. The report finds that there has been a significant increase in private sector humanitarian aid during the decade 1995–2005, with the most important increases occurring in the latter half of this period (i.e. post-2000). Of course, these trends have been significantly boosted by the ‘tsunami effect’, which could be considered to be an outlier in terms of the massive humanitarian response it attracted, both in financial terms and in the number of humanitarian actors that became involved. Yet even if one were to exclude the 2005 data, the significant positive trend in private sector humanitarian aid is still clearly discernible. Total humanitarian aid would still have increased by a factor of 1.5, while private sector humanitarian aid would have increased by a factor of two. Therefore, even without the tsunami year, both total humanitarian and private sector humanitarian aid increased substantially in the five years from 2000.