This open access book provides a unique way of documenting traditional Sámi knowledge that has survived almost 300 years followed by today’s analysis of the modern state of Sámi reindeer husbandry. Reindeer herders’ knowledge, their language and ways of managing the herds have hardly changed over the past centuries. It is the same ancient knowledge that now forms the basis for how reindeer herders think and carry out their operations. The book shows sustainable reindeer husbandry—with long continuity in knowledge and practices—which is still used today. It gives an overview of the knowledge systems and technical language of an ancient industry that has survived through millennia and is still crucial today.Our vision with this book is to highlight the long perspectives of Sámi reindeer herders’ indigenous knowledge based on what Knud Leem did at the beginning of the eighteenth century. The content is based on Knud Leem's translated version of Description over Finmarkens Lapper, their language of language, lifestyle and past idolatry.There is a direct need for this unique material to be published in English to provide access to the knowledge of the time to a wider audience. In the rest of the world, the eighteenth century is getting more and more attention in both national and international research: it is in this period that modern ways of thinking about religion, politics, science, and society find their form. Movements and ideas from the eighteenth century are important as they structure our ideas and discussions to this day. Therefore, Knud Leem's descriptions of the Sámi in the eighteenth century will also be important today and in future. Leem was a unique researcher of his time as he collected all material in Sámi.