The emergence and spread of mobile colistin (COL) resistance (<i>mcr</i>) genes jeopardize the efficacy of COL, a last resort antibiotic for treating deadly infections. COL has been used in livestock for decades globally. Bacteria have mobilized <i>mcr</i> genes (<i>mcr</i>-1 to <i>mcr</i>-9). Mcr-gene-containing bacteria (MGCB) have disseminated by horizontal/lateral transfer into diverse ecosystems, including aquatic, soil, botanical, wildlife, animal environment, and public places. The <i>mcr</i>-1, <i>mcr</i>-2, <i>mcr</i>-3, <i>mcr</i>-5, <i>mcr</i>-7, and <i>mcr</i>-8 have been detected in isolates from and/or directly in environmental samples. These genes are harboured by <i>Escherichia coli</i>, <i>Enterobacter</i>, <i>Klebsiella</i>, <i>Proteus</i>, <i>Salmonella</i>, <i>Citrobacter</i>, <i>Pseudomonas</i>, <i>Acinetobacter</i>, <i>Kluyvera</i>, <i>Aeromonas</i>, <i>Providencia</i>, and <i>Raulotella</i> isolates. Different conjugative and non-conjugative plasmids form the backbones for <i>mcr</i> in these isolates, but <i>mcr</i> have also been integrated into the chromosome of some strains. Insertion sequences (IS) (especially IS<i>Apl1</i>) located upstream or downstream of <i>mcr</i>, class 1-3 integrons, and transposons are other drivers of <i>mcr</i> in the environment. Genes encoding multi-/extensive-drug resistance and virulence are often co-located with <i>mcr</i> on plasmids in environmental isolates. Transmission of <i>mcr</i> to/among environmental strains is clonally unrestricted. Contact with the <i>mcr</i>-containing reservoirs, consumption of contaminated animal-/plant-based foods or water, international animal-/plant-based food trades and travel, are routes for transmission of MGCB.