Comparison of field- and laboratory-derived rates of chemical weathering is generally regarded as unsatisfactory. However, laboratory dissolution rates for calcite derived under realistic conditions which simulate the field situation compare well with field rates of measured limestone erosion, provided appropriate adjustments are made for periods of wetting. For physical and biological weathering there are far fewer field and laboratory studies available, and the range of different processes and process interactions makes comparisons difficult. However, period of wetting seems also to be a vital factor in more realistic comparisons between laboratory and field results. Experiments and field observations that look at the combined action of chemical physical and biological weathering are increasingly required.