Plasmid isolation denotes the experimental procedure by which covalently closed circular plasmid DNA is separated from the chromosomal DNA, RNA, proteins, and other cellular constituents of a bacterial host, yielding a plasmid preparation sufficiently free of contaminants for downstream molecular manipulation ^[1]. The procedure exploits the topological and size difference between the supercoiled plasmid molecule and the much larger, linear chromosomal DNA: under alkaline conditions in the presence of a detergent, both species are released from the cell and their hydrogen bonds are disrupted, but the two strands of the covalently closed plasmid remain topologically intertwined and in close proximity, whereas the chromosomal strands, being enormously long and bound to cellular structures, cannot readily find their complementary partners ^[1][2]. Upon neutralization with an acidic salt, the chromosomal DNA and associated denatured proteins and lipids coagulate into an insoluble aggregate that is removed by centrifugation or filtration, while the plasmid DNA, having reannealed into its double-stranded closed circular form, remains in the soluble fraction ^[2]. The term encompasses the entire preparative workflow—cell harvesting and resuspension, alkaline lysis, neutralization and clarification, and final purification of the plasmid DNA—and spans preparative scales ranging from analytical “miniprep” quantities for clone screening to large-scale manufacturing of transfection-grade or clinical-grade plasmid DNA ^[3][4]. Contemporary implementations integrate the lysis chemistry with solid-phase capture on silica membranes under chaotropic conditions or with anion-exchange chromatography, which retain plasmid DNA while permitting residual RNA, protein, and endotoxin to be washed away before elution of the purified species ^[4][5].