Modern aerospace structures see increasing use of combinations of thermoplastic and thermoset composite components, requiring the development of efficient joining methods for dissimilar matrix materials. This study aimed to investigate the Mode I fracture toughness and performance of resistance-welded and co-bonded thermoset-thermoplastic composite joints for primary aerospace structural applications. Double cantilever beam and single lap shear trials were performed. It was found that using resistance welding, a significant improvement in the Mode I fracture toughness of approximately 360 % - 520 % over co-bonding can be achieved. Single lap shear tests did not allow any conclusion about the bond strengths due to thermoset laminate failure. Although, combined with optical microscopy of the fracture surfaces, it was possible to show that significant thermal degradation of the thermoset matrix can be avoided. @en