This book stems from the results of an interdisciplinary European Union supported research project, WreckProtect, which investigated the decay and preservation of wooden shipwrecks under water in the Baltic Sea. It is not limited to the decay of wrecks in the Baltic alone and is aimed at all stakeholders with a vested interest in the protection of the underwater cultural heritage including marine archaeologists, conservators, engineers, and students in related fields at universities around the world. The book includes chapters on the anatomy and structure of wood and the physical and biological decay of shipwrecks under water. Well-known shipwrecks in the Baltic Sea are introduced, focusing upon their state of preservation and are compared to finds typically found in the North Sea and the Mediterranean. Microbial decay processes and their identification in both sediments and the water column are also discussed and related to other natural decay processes, as well as human impacts. Finally, a summary of available methods for the in-situ protection of wrecks is presented and a cost-benefit analysis of in-situ preservation versus conventional raising and conservation is given.