 The study shows that the high harmonic spectrum emitted by single-layer graphene irradiated by an ultra-short intense infrared laser pulse exhibits typical non-perturbative spectral features including a harmonic plateau and cut-off for mid-infrared driving fields at fluences below the damaged threshold. The results are derived from numerical integration of the time-dependent Schrodinger equation using a nearest neighbor tight-binding description of graphene and reveal a mechanism for harmonic emission in graphene different from that reported in atoms molecules and finite-gap solids. This article was authored by Oscar Zorin, Antonio Picon, and Luis Plagia.