This is the main Tsunami Evaluation Coalition evaluation of needs assessment during the tsunami response, focusing on the needs assessment's adequacy, appropriateness, and effectiveness during the first three months after the tsunami and its impact on the response of international agencies and institutional donors – and, ultimately, on the affected populations. Over 300 actors from over 50 agencies were interviewed in Indonesia, Sri Lanka, Thailand, and seven donor countries. National consultants and research associates assisted in the review of approximately 200 reports prepared in the first months after the tsunami. Non-structured interviews with 135 affected individuals were also conducted during field visits. The main body of this report reviews assessments intended to influence the decision making of the international community at large. Most findings focus particularly on UN or interagency reports, as needs assessment from the Red Cross movement were not formally available to the evaluators. Selected sectoral or thematic assessments – on health, water and sanitation, food and nutrition, livelihood recovery (in particular fishing) and shelter – are reviewed in greater depth in the annexes to this report.