Developing countries differ greatly in their potential for development and in the challenges they face. In one respect, however, many share a common problem: too little aid from too many donors. This report traces up to 3 700 aid relationships between all 151 aid recipient countries and the 46 largest donors, covering all members of the OECD Development Assistance Committee (DAC) and the largest multilateral agencies. This complex reality is often referred to as fragmentation of aid. This 2009 report examines the concept of aid fragmentation across countries, and what has happened since the adoption of the Paris Declaration. It also proposes measures for concentration and fragmentation, and options for tackling excessive fragmentation. Where a donor-partner aid relation is not considered non-significant from either the donor’s or the recipient’s point of view, there is an opportunity for some rationalisation. This report shows that a decrease of 23% in the number of relationships is possible when only 4% of aid is reorganised. This reorganisation, in turn, would lead to an increase in the volume of the average donor-partner aid relation of 30%.