The decay of a false vacuum of unbroken B-L, the difference of baryon and lepton number, is an intriguing and testable mechanism to gen- erate the initial conditions of the hot early universe. If B-L is broken at the grand unification scale, the false vacuum phase yields hybrid inflation, ending in tachyonic preheating. The dynamics of the B-L breaking Higgs field and thermal processes produce an abundance of heavy neutrinos whose decays generate entropy, baryon asymmetry and dark matter.