A new generation of high power laser facilities will provide laser pulses with extremely high powers of 10 petawatt (PW)and even 100 PW, capable of reaching intensities of 1023W/cm2in the laser focus. These ultra-high intensities arenevertheless lower than the Schwinger intensityIS=2.3×1029W/cm2at which the theory of quantum electrodynamics(QED) predicts that a large part of the energy of the laser photons will be transformed to hard Gamma-ray photonsand even to matter, via electron–positron pair production. To enable the investigation of this physics at the intensitiesachievable with the next generation of high power laser facilities, an approach involving the interaction of two collidingPW laser pulses is being adopted. Theoretical simulations predict strong QED effects with colliding laser pulses of>10 PW focused to intensities>1022W/cm2.