Recently there has been a strong interest in the development of solid Li-ion electrolytes for use in batteries that have higher energy and increased safety compared to the current Li-ion batteries. One such battery is an all-state-state battery with a Li anode. The major requirements for the solid Li-ion electrolyte are: high Li-ion conductivity, low electronic conductivity, and chemical/electrochemical stability with the Li metal anode/cathode. One such solid electrolyte that meets many of these requirements is cubic Li-garnet of nominal composition Li₇La₃Zr₂O₁₂ (LLZO). However, there is another important requirement. LLZO must also exhibit adequate and reliable mechanical properties. Mechanical properties of the LLZO solid electrolyte are important for the manufacture, assembly and operation of the cell/battery. For the case of operation, it is known that as the fracture strength of the electrolyte is increased this allows for a thinner electrolyte leading to lower cell resistance, higher power output during discharging and also higher energy density. There is recent work which suggests that the critical current (current at which dendrites form during charging, leading to cell failure) for a solid electrolyte with a solid metal anode is related to the fracture strength/fracture toughness of the solid electrolyte, increasing with increasing fracture strength/fracture toughness. Thus, it is imperative to determine and understand the mechanical properties of LLZO and to relate them to the structure/microstructure. It is the purpose of this talk to present the mechanical properties of LLZO as function of structure/microstructure and their relevance to cell operation. The mechanical properties that will be covered include the room temperature elastic (e.g., modulus), plastic (e.g., hardness) and fracture (fracture strength/fracture toughness) and high-temperature creep.