Publisher Summary This chapter describes the quality and agronomic use of compost. The main positive aspect of compost use in agriculture is probably related to the sustainability of this practice. The application of compost to soil is of considerable interest as a means of maintaining a suitable soil structure, as well as a means of adding organic material to soil whose organic matter content has been reduced by the practice of intensive agriculture. The concentration of nitrogen in compost is probably the most interesting from either an environmental or an agronomic point of view and this is the reason for using N content as the basis for calculating the application rates of compost. Soil water and thermal regime influence the redox processes of heavy metals and the more general decomposition processes of compost organic matter. The depth of soil tillage also is important because it determines the nature of the contact and the reactions between metals and soil constituents. The variety and complexity of physico-chemical and biological components in compost and in a soil system affect the possibility of studying the effects of the addition of organic materials into the soil.