Expectations on solid-state lithium batteries are at their highest as they are seen as a “next-generation” technology, although solid polymer electrolytes have already enabled the commercialization of electrical vehicles for almost 10 years. These are powered by lithium metal batteries and use a polyethylene oxide (PEO)-based electrolyte. Thus, after a quick review of the current state of the art on lithium batteries including various polymers electrolytes, we present some fundamentals about the lithium metal anode. We then give an overview of the different approaches that have been proposed in the past 40 years for improving the performance of these types of electrolytes. The trends that have led to the current generation of solid polymer electrolytes are reported first: They consisted in decreasing the crystallinity of PEO and increasing its chain segmental mobility while preventing electrolyte creeping at high temperature, and the use of plasticizers, fillers, statistical copolymers, and branched polymers such as cross-linked and comb-shaped polymers was developed. However, PEO and “dry” solid polymer electrolytes incorporating dissolved lithium salts, in general, suffer from intrinsic limitations. Thus, we then present as perspectives, the most promising polymer electrolyte concepts for improving lithium metal polymer batteries. In particular, the use of polycarbonates as alternative polymer matrixes, the use of polymers in hybrid organic/inorganic electrolytes, the use of block copolymers and liquid crystals for decorrelating conductivity from mechanical properties, and finally, the development of single-ion conductors.