structed from a general variational-asymptotic framework. The results of the theory are contained in closed-form expressions for the stiffness matrices of single- and double-celled composite thin-walled beams. The accuracy of the approach is demonstrated by several examples. The most important feature of these solutions,which distinguishes them from those previously published in the literature,is that shell bending strain measures are consistently taken into consideration. This is shown to be important for correct treatment of certain closed-cell configurations,the torsional stiffness of which can be off by a factor of two when bending strain measures or hoop moments are neglected. Correlation of the present formulae with finite element analysis is demonstrated to be excellent.