Traditional CdSe-based colloidal quantum dots (cQDs) have interesting photoluminescence (PL) properties. Herein we highlight the advantages in both ensemble and single-nanocrystal PL of colloidal CsPbBr 3 nanocrystals (NCs) over the traditional cQDs.A ne nsemble of colloidal CsPbBr 3 NCs (11 nm) exhibits ca. 90 %P Lq uantum yield with narrow( FWHM = 86 meV) spectral width. Interestingly, the spectral width of as ingle-NC and an ensemble are almost identical, ruling out the problem of size-distribution in PL broadening. Eliminating this problem leads to an egligible influence of self-absorption and Fçrster resonance energy transfer,a long with batch-to-batch reproducibility of NCs exhibiting PL peaks within AE 1nm. Also,PLpeak positions do not alter with measurement temperature in the range of 25 to 100 8 8C. Importantly,C sPbBr 3 NCs exhibit suppressed PL blinking with ca. 90 %o ft he individual NCs remain mostly emissive (on-time > 85 %), without muchi nfluence of excitation power.The CsPbX 3 (X = Cl, Br,o rI )p erovskite was reported by Møller in 1958.[1] Mitzi and co-workers showed the interesting optoelectronic properties of organic-inorganic perovskite materials about twenty years ago. [2] In about the last six years,s olution-processed organic-inorganic hybrid perovskites,s uch as CH 3 NH 3 PbI 3 ,b ecame one of the most celebrated materials because they exhibit nearly 20 %s olarcell efficiency.[3] This success of bulk perovskite,a lso prompted af ew reports on colloidal nanocrystals (NCs) of MPbX 3 (M = CH 3 NH 3 and Cs;X = Cl, Br, and I), where intense photoluminescence (PL) has been the main property.[4] Herein, we establish that PL from CsPbBr 3 perovskite NCs is intrinsically different and advantageous,c ompared to that from traditional colloidal quantum dots (cQDs).State of the art, highly luminescent CdSe-based cQDs, particularly,c ore-shell NCs found applications in highdefinition displays because of the narrower full width at half maxima (FWHM) of their PL compared to that of organic dyes.[5] Kovalenko et al. [4b] reported early this year that CsPbX 3 (X = Cl, Br, and I) NCs exhibit around 90 %P L efficiency with narrow FWHM, which is superior to most CdSe-based NCs obtained even after surface modifications. Tr aditional CdSe based cQDs exhibit intense PL only when the size of NC (ca. 5nm) is comparable to the Bohr excitonic diameter, where strong quantum confinement of charge carriers enhances the transition probability.T his requirement of quantum confinement, however,r esults into spectral broadening from the size-distribution, and ah igh density of trap states because of the large surface to volume ratio. [6] Owing to the size-distribution problem where smaller sized NCs exhibit higher optical gap compared to larger sized ones,c hromaticity and quantum yield (QY) of PL changes with concentration of NCs because of both self-absorption and Fçrster resonance energy transfer (FRET).[7] Also,since the optical gap of such luminescent cQD is strongly dependent on the size of the NCs,reprodu...