Semiconductor nanolasers represent a modern frontier of research at the intersection of nanotechnology, nanophotonics, and laser physics. In this review, we examine some of the most exciting recent results in this field. We focus on nanoscale lasers fabricated using two- dimensional photonic crystals and discuss the characteristics of these nanolasers. Due to the small size and strong field localization of these nanolasers, some common concepts in semiconductor laser physics must be reconsidered to to validate their applicability at the nanoscale. We attempt to answer the question of how small a laser can be and whether there is a limit to its size.