We study the stability of the rare-earth dopant, Eu, in metal-halide perovskite CsPbBr3 with cubic and orthorhombic structures from first-principles calculations. In these perovskites, Eu is substitutionally doped on Pb sites because of their comparable ionic sizes which lead to only a small strain in the doped system. Accordingly, our results show that the cost of Eu doping is quite small compared to the values in other common hosts such as GaN. This makes these perovskites excellent candidates to develop rare-earth doped semiconducting materials for bright luminescence as it has also been observed recently in the case of thin films of CH3NH3Pb1-xEuxI3, Eu-doped quantum dots of CsPbBr3, and nanocrystals of CsPbCl3 in addition to their outstanding properties for applications in solar cells. © 2019 American Chemical Society.