On offshore wind turbine structures, grouted connections are widely used to connect the tower structure to the foundation while accommodating the unavoidable geometrical tolerances effectively. The long-term behaviour of high- and ultra-high-strength grouts primarily depends on the adequate strength and durability of the material plus the process reliability. The performance of the fresh and the hardened grout is influenced by many factors that have to be evaluated and considered individually with respect to the “rough” offshore conditions. Those factors are: mix performance and consistency, the ambient conditions at the place and time of use, the equipment for and stability of the mixing and casting processes, the length of casting time and the thermal and mechanical loads during the early stages. To ensure adequate long-term behaviour, a meaningful quality assurance system should be set up to cover both the materials and the processes. The article emphasises some fundamental experiences gained by the authors with numerous wind turbine parcs in the North Sea and the Baltic Sea.