The bloomery iron production method, which was in general use in medieval time, is presented in some detail. It is discussed how slags are formed, and how production slags and purification slags may be distinguished. The slag-analytical method is introduced and is applied on a large number of iron objects from ancient Norse and Inuit sites. Particular emphasis is placed on scanning electron microscopy and microanalysis of the minute slag inclusions in the artefacts. It is shown that a major part of the iron objects on Norse sites was probably made from Norwegian iron ores, and arrived as finished products from Norway. The presence of a few purification slags in the Eastern and Western Settlements prove, however, that raw blooms were sometimes shipped from Norway and afterwards finished by smithing in Greenland. The present study does not support the theory that primary iron production took place in the Norse settlements. A number of iron tools on Inuit sites are shown to be of Walloon origin, having arrived on whaling and expedition ships since the late 16th century. It is argued that many of the harpoon heads and knives were forged by the ships' blacksmiths according to the desires of the Inuit. Walloon iron was also present in Haabetz Colonie in 1721 A.D. Some puddled iron nails were identified in Washington Land. They are probably relics from some 19th century American expedition. Finally, the northern-most and largest iron meteorite tool ever found, a lancehead, was identified in Washington Land. Also, a meteoritic arrowhead was identified in the Western Settlement. The arrowhead was made from Cape York meteoritic iron and must have been traded to the Norsemen before 1350 A.D.