The aim of this thesis is to investigate the local and global buckling behaviour of delaminated composite plates using exact stiffness analysis. Several attempts are made to model delamination with the accuracy of detailed 3D finite element analysis (FEA) but substantially improved computational efficiency. Investigation of local buckling behaviour is performed using the exact stiffness program VICONOPT, giving good comparative results and substantially less solution times compared to those of FEA. Extending this approach to global buckling behaviour poses limitations and difficulties in retaining computational efficiency. Several techniques are introduced to study global buckling behaviour while requiring less solution time than FEA. The advantages and disadvantages of these techniques are discussed. Finally, an improved smeared stiffness method is derived which results from simplification of the total potential energy expression for the plate. This simplification avoids expensive computational effort while maintaining results of good accuracy (within 2%-3% of FEA results). This method can be employed for modelling delaminations of different shape and size located anywhere in the composite plate.