To evaluate the impact of management practices on soil environment it is necessary to quantify the modifications of soil structure which is one of the most important properties affecting crop production because it influence the depth to which roots can penetrate, the volume of water which can be stored, and the movement of water, air, nutrients and soil fauna. The effect of tillage on soil organic matter, on soil water content, on soil aggregation, on soil aggregate  stability, on soil porosity, on soil crusting and on soil compaction are discussed. The quantification of soil porosity is fundamental to characterize soil structure and now it is possible because of the increasing use and availability of the technique of image analysis that allows the measurements of soil porosity on thin sections or impregnated soil blocks, prepared from undisturbed soil samples. Generally the reduced tillage practices seems the most appropriate to maintain favourable soil conditions and to prevent soil structure degradation.