Soils are three-phase systems which undergo changes as soon as the external stresses exceed the internal soil strength, defined by the precompression stress value. The three-dimensional stress propagation induces corresponding volumetric soil strain. Soil compaction can result either in a higher bulk density or, when soil loading is attended with retarded water fluxes and high dynamic forces, in a completely homogenised soil characterised by a lower bulk density and a predominance of fine pores. While in natural soils the structure can be described as macroscopically homogeneous, less careful mechanical treatment or reduced addition of organic substances results in less favourable types of soil aggregates. As a result of applied external stresses, physical and chemical processes, such as mass flow and diffusion of water, ions and gases, are at least retarded or even completely altered. Both increased bulk density and homogenisation cause decreased aeration and increased penetration resistance, which results in impeded root development. Reduced water permeability may result in soil erosion, with serious negative effects on the environment. Compacted soil may also contribute to global atmospheric warming due to increased emission of CO2, CH4 and N2O from such soils. Anthropogenic changes in soil structure and soil functions remain constant for extended periods of time and efforts to restore deteriorated soil structure very often fail because of excessive loosening and homogenisation, cultivation of too wet soil or, afterwards, ill-adapted soil management practices, resulting in even worse soil properties. The present paper gives a summary of relevant work performed by the authors.