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Classical and recurrent nova explosions occur on top of white dwarfsaccreting H-rich matter from a companion main sequence or red giant star, in aclose binary system. In the recent years, since the launch of the Fermigamma-ray satellite by NASA in 2008, several novae have been detected byFermi/LAT (LAT: Large Area Telescope) in high-energy (HE) gamma rays, withenergies larger than 100 MeV. This emission is known to be related to theacceleration of particles in the internal and/or external shocks occurringearly after the thermonuclear nova explosion. However, very-high-energy (VHE)gamma-rays, with energies larger than 100 GeV, produced as a consequence ofnova explosions have only been discovered very recently, in the recurrent novaRS Oph, that had an outburst in August 2021. These require the acceleration ofprotons, and not only of electrons; this was in fact predicted theoretically -based in observations at other wavelengths - in the previous eruption of RSOph, in 2006, but has not been confirmed observationally until now. We reviewthe origin of the different types of gamma-ray emission in novae and highlightthe relevance of the recent VHE gamma-ray emission discoveries for the novatheory, mainly in the field of the mass ejection and the associated particle(electrons and protons) acceleration processes.

Nova explosions -- The fascinating gamma-ray emitting recurrent nova RS Ophiuchi