  Novae had not been widely considered as high-energy (>100 MeV) gamma-ray
sources before the launch of the Fermi Large Area Telescope (LAT). In March
2010, the LAT made the first gamma-ray detection of a nova in the symbiotic
binary V407 Cygni. The LAT observations uniquely probed the high-energy
particle acceleration mechanism in the environs of the V407 Cyg binary system
consisting of a white dwarf and its red giant companion. Subsequently in June
2012, two more novae were detected with the LAT, Nova Sco 2012 and Nova Mon
2012, thus heralding novae as a new gamma-ray source class. For Nova Mon 2012,
the gamma-ray transient source was discovered first, followed by the optical
confirmation of the nova, showcasing how novae can be found with the LAT
independently from traditional optical searches. We discuss the LAT detected
gamma-ray novae together with observational limits on other optical novae over
the first four years of the Fermi mission and reconsider the possible
high-energy gamma-ray production mechanisms in novae in light of the new
detections.
