Accurate and complete information is needed to guide the formation, implementation, monitoring and assessment of agricultural policy. Obtaining both qualitative and quantitative information is vital for ensuring that policy measures are targeted, efficient and cost effective. Quantification of impact and benefit-cost analysis are only possible if information of sufficient quantity and quality is available. Meeting this requirement is increasingly challenging due to an expansion in the range and complexity of policy concerns associated with agriculture. Problems can be posed by a lack of knowledge about technical relationships that underlie key processes, by the inherent uncertainty of outcomes or difficulties in monitoring these, and by information asymmetry (i.e. situations in which the information necessary to inform policymaking exists but it is difficult or costly to obtain). This study examines information needs to guide the formation, implementation, monitoring and assessment of policies for agriculture, outlines deficiencies, argues for selective improvements in data availability, quality and relevance in order to satisfy policy priorities, and suggests ways to achieve these. Methods for dealing with remaining deficiencies when designing and implementing policies are also outlined...