Constant amplitude fatigue crack propagation rate (da/dN) data are provided for a wide range of low and medium strength steels in the form of plate and a forging. The ultimate tensile strength of the materials is less than 850 MN/sq m and their thicknesses range from 5 to 70 mm. The data have been derived from tests conducted in laboratory air at room temperature and mean da/dN curves are presented in terms of the stress intensity factor range and the stress ratio, R. The materials are grouped according to four ranges of their 0.2 per cent proof stress and where possible the upper limit of scatter of the data is also provided. The range of da/dN covered is from 10E-8 m/cycle down to the threshold at 2x10E-11 m/cycle. The effects of variations in mean stress, specimen size and thickness, and material yield strength are discussed. Details of all the materials and types of test specimen are tabulated and summary da/dN curves that compare the different groups of materials are given. Curves showing the effect of variations in the value of R at threshold for the various materials are also presented. Simple worked examples illustrate how the data may be used in practice.