Cell-free protein expression or cell-free protein synthesis (CFPS) refers to the protein expression approach that produces target proteins without using living cells. All the cellular machinery, such as ribosomes, enzymes, tRNAs, amino acids, and cofactors, are contained in CFPS for direct protein synthesis. A supplied nucleic acid template can be transcribed and translated in CFPS, and this process is not constrained by a cell wall or homeostasis conditions required to maintain cell viability.