This paper reviews recent advances in the research and development toward the graphene-based terahertz (THz) lasers. Mass-less Dirac Fermions of electrons and holes in gapless and linear symmetric band structures in graphene enable a gain in a wide THz frequency range under optical or electrical pumping. The excitation of the surface plasmon polaritons in the population-inverted graphene dramatically enhances the THz gain. Photon-emission-assisted resonant tunneling in a double-graphene-layered nano-capacitor structure also strongly enhances the THz gain. Novel graphene-based heterostructures using these physical mechanisms for the current-injection driven THz lasing are discussed. Their superior gain-spectral properties are analyzed and the laser cavity structures for the graphene THz laser implementation are discussed.