For centuries, wooden pile constructions support buildings in areas with unstable soils in Europe, and many other parts of the world. Depending on the local soil conditions and the building above, pile foundations differ in construction type, pile length, timber species and timber quality applied and the degree of conservation. It is estimated that millions of wooden foundation piles are still in service, carrying small buildings like family houses, or bigger buildings like churches and palaces or constructions in water-like quay walls or bridges. Many of these buildings are old and therefore wooden foundations are an important asset for cultural heritage. This is not always realised probably because foundations are hidden in the soil and therefore not visual as part of the building and because the wooden pile is replaced by concrete from the 1950s and onwards. There are many examples of wooden foundations that have been in service for several hundreds of years, but there are also examples of severe settling of buildings founded on wooden piles in historical town cities like Amsterdam or Venice. All foundation problem causes are known and are explained in this article. However, the process of bacterial wood decay, one of the causes, is not yet fully understood and the immense population of wooden foundation piles in the European soil offers a unique chance to learn more about it. As bacteria can degrade wood under water, it is also one of the main threats of waterlogged archaeological wood. A better understanding of bacterial wood decay does not only give chances to improve the conservation of wooden foundations, but it can also improve the in situ conservation of wet archaeological sites. Conservation of wooden foundation piles does not only save the building above its construction but saves also a unique archive related to building history and past timber trade connections. This article advocates the importance of foundation piles on the cultural heritage agenda as key issue for wood conservation in wet soils and saving a huge building historical achieve.