Antimicrobial resistance (AMR) is the ability of microorganisms that cause disease to withstand attack by antimicrobial medicines. From drugs used to treat common bacterial infections, to the complex combinations now fighting HIV infection, resistance is increasingly being detected and is spreading rapidly. In some parts of the world, once powerful medicines against malaria and tuberculosis have now become virtually useless. AMR is rapidly becoming a major public health risk and is threatening to undo decades of advances in our ability to treat disease. It is challenging our whole understanding of how we control communicable disease.