Although much has been written on the history of the requirement of proof of crimes beyond a reasonable doubt, this is the first study to probe the history of its civil counterpart, proof by a preponderance of the evidence. It turns out that the criminal standard did not diverge from a preexisting civil standard, but vice versa. Only in the late eighteenth century, after lawyers and judges began speaking of proof beyond a reasonable doubt, did references to the preponderance standard begin to appear. Moreover, United States judges did not start to instruct juries about the preponderance standard until the mid-nineteenth century, and English judges not until after that. The article explores these developments and their causes with the help of published trial transcripts and newspaper reports that have only recently become accessible. The history thus revealed casts a new light on two subjects that have aroused much scholarly attention during the last few years: the fact that European civil law systems do not proclaim differing standards for civil and criminal proceedings; and the questionable policy foundations on which the preponderance standard rests.