Garnet-type lithium ion conductor is a promising candidate of solid electrolyte on the way towards all-solid-state lithium ion batteries. This short review presents the latest efforts on the stability of lithium garnet against ambient air, lithium metal, cathodes, and liquid electrolytes. The discussion on the air stability includes the reaction mechanisms as well as the effects of material properties and environmental parameters. The interface stability with Li metal and cathode materials covers both thermodynamic computation and experimental results. The Strategies to reduce the garnet/Li interfacial impedance and to subsequently suppress the Li dendrite formation are highlighted. The last section on "hybrid electrolyte" discusses the stability of lithium garnets in liquid electrolytes, namely aprotic and aqueous electrolytes.