Decision makers need the right information at the right time but in rural development much information generated is too costly and inappropriate. Rapid rural appraisal forms part of the attempt to learn about rural conditions in a cost effective way. Such appraisal involves avoiding the traps of quick and dirty or long and dirty methods and using instead methods that are more cost effective. To do this means ignoring inappropriate professional standards and instead applying a new rigour based on the two principles of optimal ignorance—knowing what it is not worth knowing—and proportionate accuracy—recognising the degree of accuracy required. The article reviews a range of approaches and techniques for rapid rural appraisal that are less rigid and exhaustive than many traditional methods and yet more rigorous in relation to cost and use. Time is emphasized as a critical factor in effective appraisal and rapid rural appraisal methods increase the chance of reducing the bias against the poorer rural people in the promotion of rural development.