Antibiotic-resistant infections are a major threat to global public health and there is an urgent need to develop new drugs and interventions to treat and prevent infections caused by antibiotic-resistant bacteria. The human gut microbiota harbours both commensals and opportunistic pathogens which can acquire resistance to antibiotics through mutation and horizontal gene transfer. The powerful combination of modern high-throughput DNA sequencing and microbiological culture methods is providing novel insights into the mechanisms of antibiotic resistance among, up to recently poorly studied, commensal bacteria in the gut. Interventions to minimise the abundance of antibiotic-resistant commensals and opportunistic pathogens include faecal microbiota transplantation and the use of live biotherapeutics, but the efficacy of these treatments remains elusive.