A background review of soil compaction processes is presented and theoretical relationships among loads, pressures and soil moisture are discussed. Research directions and needs for the future are outlined.THE EFFECT OF SOIL COMPACTION, especially below normal tillage depths, is a major agricultural concern today. In general, heavy axle loads on moist soil is the primary cause of excessive compaction, But important questions remain: How heavy? How wet? Do low pressure high flotation tires help?