Recent developments in herbicides and machinery for drilling and cultivation require a reassessment of tillage requirements in terms of soil physical conditions, since these may determine to what extent current or new systems of reduced or zero tillage can be more widely adopted. Soil and climate conditions frequently interact in Britain to give obviously unfavourable soil conditions particularly where heavy machinery is in use. A review of the physical conditions of field soils under different tillage systems shows that reduced or zero tillage cannot yet be recommended for the more demanding crops and less well drained soils.