ESDU 83023 provides more than 1750 plane strain fracture toughness values for 39 UK and US low alloy, nickel, maraging and stainless steels. The data are presented in tabular form, providing details of test temperature, crack orientation with respect to grain flow, proof stress, chemical composition and heat treatment. All the data relate to non-corrosive environments at temperatures from -200 to 150 degrees C (-328 to 302 degrees F). Typical dependence of fracture toughness and proof stress on temperature is illustrated graphically. After a brief explanation of the importance of plane strain fracture toughness in design, test conditions, presentation of data and factors that affect fracture toughness are discussed. The method is explained by which statistical analysis is applied to the data to obtain with a chosen confidence design allowable values of fracture toughness. Empirical relationships between fracture toughness and Charpy values are discussed and two general correlations given together with seven others that give good results with specific steels. A practical worked example illustrates the use of the data.