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Lithium-ion polymer (LiPoly or LiPo) cells first appeared in consumer electronics in the mid-1990s. The technology for these devices evolved from previously established lithium-ion (Li-ion) cells. The difference between the two lies in the electrolyte; in Li-ion batteries it consists of a lithium salt dissolved in a low molecular weight solvent, whereas a LiPo electrolyte is a polymer gel network. Substitution of liquid electrolyte by a solid analogue allows simplification of the cell structure and many restrictions in terms of architecture and safety are eliminated. Three decades of research and development of solvent-free polyether-based electrolytes has seen many advances, but barriers still remain, restricting their commercial exploitation. Commercial viability was realized in polymer gel electrolytes, a compromise between the liquid and solvent-free systems. The all-solid-state LiPo concept translates into a battery that can be shaped to suit the device it will power, is lighter, and can undergo denser packaging than its liquid electrolyte counterpart. The battery energy density is potentially much greater than that achieved by competing cell chemistries, including the Li-ion cell. With recent advances in LiPo cell technology, the commercial balance between the Li-ion and LiPo systems is expected to shift in favor of the latter.