The transverse cracking in glass-fibre composites based on (i) an unmodified epoxy resin system, (ii) a flexibilised epoxy system and (iii) an epoxy containing an elastomeric toughening agent, was studied under direct tensile loading and repeated tensile loading at room temperature, 75ºC and 100ºC. It was found that when the resin is in the glassy state, the final crack spacing and the relationship between stress and crack spacing can be explained in terms of shear stress transfer from the longitudinal plies. If the toughness of the resin is sufficient to allow slow crack growth, a more closely spaced array of irregular cracks is formed. The elastic modulus of the laminate is lowered by transverse cracking, but the modulus in both the cracked and uncracked state is not greatly affected by the modulus of the resin. The high ductility of the resins in the rubbery state is not sufficient to prevent transverse cracking although, because of the very low modulus of the resin in this state, such cracking is not accompanied by large reductions in the stiffness of the laminate.