The medieval English wool trade was a commercial activity of huge economic importance. The historiography of the medieval wool trade, however, has focused overwhelmingly on its legitimate side. This article uses the evidence of legal proceedings prosecuted in the royal courts to provide the first detailed account of wool smuggling in the fourteenth century, a time of heavy governmental regulation and hugely increased taxation. It demonstrates that a substantial number of merchants responded to these challenges by participating in a flourishing trade in smuggled wool which was considered a serious threat to crown fiscality. In particular, the article explores how smaller-scale smuggling took place along under-regulated areas of coastline away from customs ports; how major export operations were able to smuggle wool through the customs system itself; and how concerns over smuggling influenced a series of administrative reforms designed to improve the efficiency of commercial regulation.