The ability of bacteria to survive drugs that once killed them, developed through mutation and gene sharing under the selective pressure of antibiotic use. It is among the gravest threats to modern medicine and food safety alike: resistant Salmonella, Campylobacter, and E. coli from animals and food cause infections that are harder and costlier to treat. Agricultural antibiotic use, particularly for growth promotion, has been a major driver, prompting bans and stewardship programs in many countries. Resistance genes travel on mobile DNA that jumps between bacterial species, so prudent use anywhere protects effectiveness everywhere. Surveillance of retail meat and farm environments tracks the trends, while alternatives such as vaccines, probiotics, and improved hygiene aim to reduce the need for antibiotics in the first place.