Underpinning of foundations is one of the most rapidly growing areas of refit both in Finland as well as internationally. Throughout time, cities and villages have been founded at waterside locations: by seas, lakes and, very often, on river deltas. Geologically, the ground soil at waterside locations - mud, clay, silt and peat - compresses easily under heavy loads. What is more, early inhabitation of these sites may have created several meters of culture layers, which are also highly compressible. Rotting wood piles, the uneven sinking of cohesion piles, and subsiding natural foundations are the main reasons for underpinning of foundations. Other reasons include the need for more bearing capacity, for example, when the load on the upper structures increases, or the need for further reinforcement - for instance, to protect buildings from earthquakes in highly seismic areas. Underpinning - Nordic Practice is designed as a textbook for polytechnics and universities, but it is equally suitable for real estate owners, engineers and constructors with an interest in underpinning. The authors represent the top tier of underpinning experts in Finland.