Recent progress on rare-earth doped polycrystalline YAG transparent ceramics has made them an alternative novel solid-state laser gain material. In this paper we present results of our research on polycrystalline RE:YAG transparent ceramics. High optical quality YAG ceramics doped with various rare-earth (RE) ions such as ${\rm Nd}^{3+}$, ${\rm Yb}^{3+}$, ${\rm Er}^{3+}$, ${\rm Tm}^{3+}$, and ${\rm Ho}^{3+}$ have been successfully fabricated using the solid-state reactive sintering method. Highly efficient laser oscillations of the fabricated ceramics are demonstrated.