Experiments that can reveal the nature of the second- and the fourth-order terms in the interaction between charged particles and electromagnetic fields in vacuum have been discussed here. An attempt has been made to emphasize the successes of the experiments already completed and the promising lines of future investigation. The theoretical considerations relevant to the experiments under review have also been outlined. In all cases studied so far, the experimental results agree with the predictions of conventional quantum electrodynamics.

DOI:https://doi.org/10.1103/RevModPhys.39.52