ESDU 78021 introduces the buckling behaviour of struts and illustrates overall buckling (flexural and torsional-flexural) and local buckling modes (for various section shapes). The effect of initial eccentricity or lateral load on buckling is discussed and illustrated. The basis of theoretical methods of calculating buckling is explained and the practical interpretation of the results depending@ for example@ on end restraints or initial irregularities is discussed. A comprehensive worked example shows how ESDU data on strut strength are used to predict buckling and to calculate the post buckling strength. A table indexes the ESDU data available on strut behaviour according to section shape and buckling mode@ and indicates data also included on minimum weight design and for the effect of lateral load on buckling.