During its development and at the time that the south Wales iron industry was at its most successful the only way (other than by personal contact) in which contact between the different branches of the industry could be maintained was by letter. Thus the postal service - both the General Post Office and a multiplicity of private posts - made a vital contribution to the success of the industry which so far has received little attention. This work traces the development of the postal service in the south Wales valleys from its primitive state in the mid-18th century to what had become a recognisably modern postal service a hundred years later. It is based on information derived from the archives of the Post Office itself and of the various iron companies, from contemporary newspapers and from oral tradition recorded by later historians in the Valleys.