There is an abiding interest in using nanocrystals as laser gain media due to their tunable emission wavelengths, low cost, and solution processability. However, it has been proven difficult to achieve low lasing thresholds suitable for practical applicatons. MRSEC members Engel and Talapin showed that colloidal semiconductor nanoplatelets (NPLs) with electronic structure of quantum wells can produce optical gain and lase in the red, yellow, green, and blue regions of the visible spectrum with low thresholds and high gains, both a significant improvement over colloidal quantum dots. The lasing color is dictated solely by the NPL thickness while lateral dimension of the NPLs do not affect either the lasing thresholds or gain saturation levels. This observation highlights the qualitative difference of multiexciton dynamics in CdSe NPLs and other quantum-confined CdSe materials, such as quantum dots and rods.