The main aim of the present study was to enhance the understanding of damage evolution in wind turbine blades by a combination of structural- and material modelling. Basic damage modes were identified in wind turbines tested to failure under static andcyclic loadings. Two of the observed damage types, compression failure and crack growth along adhesive joints, were studied in details. Modelling of a load carrying composite spars as well as composite columns were performed for assessing the compressivestrength. A fracture mechanics approach was developed for prediction the strength of adhesive joints. The effect of porosity on the strength of adhesive joints was also investigated.