This thesis investigates the reclamation of mires (fens and bogs) in Sweden with a focus on the early modern period. Today, the mires are valued natural habitats and their cultivation is controversial. International research describes wetland reclamation and the related knowledge transfer between European countries already from the 12th century. In Sweden, despite some early records of reclamation of mires in the 17th century, has earlier research focused on reclamation during the 19th and 20th centuries. The aim of the thesis is to study the landscape, actors and driving forces behind the early reclamation (before 1800). Understanding the early reclamation can provide a new perspective on current views on wetlands. It is also an interesting example of how the landscape is changed constantly by people with different goals through history. The subject is studied through a multimethod approach using sources such as historical maps, diaries, 17th- and 18th-century literature and place names. The main conclusions of the study are that reclamation of mires is seen already in 17th-century maps, with local wider distribution during the 18th century. The crown and scientists expressed a growing interest in reclamation of the mires from the early 18th century. Links to Europe, in particular Holland, can be seen within this discourse. In both literature and the experimentation that took place, the Swedish migrant group, the Dalecarlians, played a key role. They shared with the early Dutch groups the practical knowledge needed in major reclamation projects. Furthermore, this study shows that a number of actors assumed at various times the role of mobile innovation spreaders. Dutch farmers and experts, labour migrants, landlords and scientists all acted to spread knowledge of mire reclamation. Ample resources, networking and geographical mobility appear to have been prerequisites for all actors, from peasants to landlords, but they had different underlying motives for the practice.