The aim of this research was to examine the use of grouting methods for pile foundation improvement, a generic term that is used here to define both foundation renovation (increasing the bearing capacity of a pile foundation that has insufficient bearing capacity) and foundation protection (safeguarding the piles of the foundation against possible damage resulting from underground construction activities in the vicinity). A full-scale test, of which the general set-up and consistency check are outlined in the thesis, examining the feasibility of foundation improvement by means of grouting techniques was conducted in Amsterdam. The main part of the thesis focuses on permeation grouting, jet grouting and compaction grouting. For each method, first some more general aspects like history, grouting equipment, grouting parameters and fields of application are outlined. Subsequently existing theories used in modelling the grouting process are examined and compared. The test results are discussed. By using the pile displacements, soil stresses, pore pressures and pile bearing capacity measured in the test, it was possible to examine the influence of grouting methods on pile foundations. The use of and suitability of geophysical verification methods for grouting, which were necessary to determine the shape and position of grouted elements, were also considered. To determine how grouting methods can best be applied for foundation renovation purposes, the cost of grouting methods and the hindrance that they cause have been compared with those of conventional foundation renovation methods. The construction cost of grouting can be up to about 50% lower than that of conventional methods of underpinning a structure. Taking cost, hindrance and the test results into consideration, it can be concluded that permeation grouting and compaction grouting are economic and effective alternatives to conventional underpinning methods for renovating pile foundations. The methods may also be used for pile foundation protection. Jet grouting is only suitable for use in the renovation of end bearing piles when the structure is strong and stiff enough to redistribute the loads from the grouted pile. Jet grouting is very suitable for use in protecting pile foundations because it can be applied in any type of soil.