Abstract: Despite many efforts, the extragalactic magnetic field (EGMF), presumed to exist in the voids of the large scale structure, remains undetected. Since the EGMF may be generated either by processes in the early universe or by outflows from galaxies, and it could supply the seed fields required by many models of galactic and cluster field formation, its properties are of interest from both cosmological and astrophysical viewpoints. I will review a recently developed technique for measuring the EGMF strength using combined gamma-ray observations from the Fermi Gamma-Ray Space Telescope and ground-based instruments such as VERITAS. The technique relies on modeling the electromagnetic cascade that develops in extragalactic space due to gamma-ray interactions with the extragalactic background light and CMB and for the first time permits the placement of a lower limit on the EGMF strength. I will describe two approaches to characterizing the cascade and discuss the interpretation of gamma-ray observations of the blazar RGB J0710+591 as limits on the existence of an EGMF-induced "halo."