Rainfall erosion is a complex process and good understanding of the mechanisms involved is necessary if inappropriate designs and procedures are not unwittingly used in rainfall erosion experiments. Numerous runoff and soil loss plots of various sizes have been installed in many parts of the world. It is essential that on any eroding surface water flows across the surface without interference from any equipment designed to collect runoff and sediment. Examples of designs that do not conform to this requirement are presented. Because sedimentation occurs in tanks, coarse material needs to be collected and measured separately from fine material which can be subsampled when suspended in the runoff water.Despite attempts to operate in areas where soil properties are uniform, replicates are shown to produce considerable variation in the soil losses produced by the same event. Slope length and gradient influence the type of erosion that occurs on a plot. Slope lengths less than one metre encourage erosion where detachment and transport is controlled by the expenditure of the energy generated by raindrop impact but as slope lengths and gradients increase, detachment by flow may result in the development of rills. Experiments on slopes of one or two metres in length do not provide data that can be used to parameterise models like the USLE that operate on slopes up to 300 m long.Rainfall simulators have been widely used in rainfall erosion experiments on plots shorter than 10 m. Given the fact that raindrop induced bed load transport is stimulated by individual raindrop impacts, spatial variations in raindrop size and impact frequency in artificial rainfall produced by sprays can lead to erroneous results. Similarly, temporal and spatial variations in flow depths in rain-impacted flows on inclined surfaces in experiments leads of variations in erosive stress that are seldom taken into account when analysing the results produced using artificial rainfall. This presents difficulties in respect to apply the results to other situations. The WEPP interrill erosion model was designed to predict soil movement from interrill areas to rills but it is shown that the ranking of soils according to their interrill erodibility varies depending on whether eroding surface is flat plot or on a ridge tillage sideslope.