Negative muons (elementary particles having a mean life of 2.2 microseconds) have been used to induce nuclear fusion reactions of the type: Behaving like a very heavy electron, a muon forms a tightly bound deuteron-triton-muon (dtµ) molecule. Fusion then ensues, typically in picoseconds, as the nuclei tunnel through the Coulomb repulsive barrier. Up to 160 fusions per muon (average) have been observed in cold deuterium-tritium mixtures. Thus, the process may be called muon-catalyzed fusion, or “cold” fusion. The fusion energy thus released is twenty times the total energy of the muon driving the fusion reaction. However, the energy needed to produce the muon catalysts is currently much larger than the fusion energy released. In preparing for muon-catalyzed fusion experiments, a number of engineering challenges were encountered and successfully resolved. Similar challenges would be faced in a (hypothetical) cold fusion reactor. High-temperature plasmas and many associated difficulties are of course circumvented. However, the gaseous d-t fuel must be contained at elevated temperatures (∼400°C) and near-liquid density. (Experiments show that increasing either parameter enhances the fusion yield.) This translates into high gas pressures (∼108Pa) and a new class of engineering challenges. Material strength and fabricability, hydrogen permeation and material embrittlement, tritium inventory and safety concerns, muon beam scattering and degradation, and reaction vessel geometries are among critical engineering considerations.