© W. S. Maney & Son Ltd 2012 DOI 10.1179/1350503312Z.00000000041 conservation and mgmt of arch. sites, Vol. 14 Nos 1–4, 2012, 479–86 Nydam Mose: In Situ Preservation at Work David Gregory and Henning Matthiesen National Museum of Denmark, Denmark The site of Nydam Mose saw the beginning of systematic research into in situ preservation of waterlogged archaeological sites on land at the National Museum of Denmark. In the past fifteen years a generic approach to in situ preservation of archaeological sites has been developed based on this research. This article is primarily a review of this generic approach, sum- marizing the methods and results with particular reference to the published results from the investigations in Nydam Mose. keywords Nydam Mose, in situ preservation, deterioration, mitigation, monitoring Introduction During the Iron Age, Nydam Mose was a small lake into which several thousand artefacts were deposited on several occasions between approximately ad 200 and 500 (Rau, 2012). The present-day site is a waterlogged water meadow and since 1859 several archaeological campaigns have taken place. The last of these was conducted in 1997 when, because of the volume of finds (over 16,000 artefacts excavated between 1989–97; Figure 1) and the resources required for their conservation, it was decided to stop further excavations and investigate the feasibility of preserving the site in situ. Over the following fifteen years a generic approach to in situ preservation has been developed which we believe can be applied when considering the in situ preservation of other archaeological sites. Approach to in situ preservation The authors use the term in situ preservation to mean a form of preventive conserva- tion whereby preservation of artefacts and cultural deposits is assured by a sequence of artefact analysis, initiation of stabilization strategies and environmental monitor- ing (Gregory and Matthiesen, 2007). In order to achieve this there are five fundamental points related to the successful in situ preservation of archaeological sites, these are: