Antibiotic resistance is a global health challenge, involving the transfer of bacteria and genes between humans, animals, and the environment. Although multiple barriers restrict the flow of bacteria and genes, pathogens recurrently acquire new resistance factors from other species, reducing our ability to prevent and treat bacterial infections. Evolutionary events leading to new resistance factors are rare and challenging to predict, but may have vast ramifications. Transmission events of already widespread resistant strains are common, quantifiable, and more predictable, but their consequences are limited. Quantifying pathways and identifying drivers and bottlenecks for environmental evolution and transmission of antibiotic resistance are key to understanding and managing the resistance crisis. The environment plays a role in resistance evolution, transmission, and as a reflection of the regional antibiotic resistance situation in the clinic. Current evidence, risk scenarios, surveillance methods, and potential drivers are discussed, along with actions to mitigate risks. Many bacterial species evolved the ability to tolerate antibiotics long before humans started mass-producing them. Isolated caves, permafrost cores, and other environments can provide insights into resistance mechanisms from the pre-antibiotic era. The competition for resources among microorganisms, including the natural production of secondary metabolites similar to antibiotics, is an important driver of resistance evolution. The introduction of antibiotics as clinical agents radically changed the preconditions for resistance evolution and spread, providing unprecedented selection pressures on human and animal microbiota and environments heavily polluted with antibiotics. This selection pressure has promoted the mobilization and horizontal transfer of antibiotic resistance genes (ARGs) to many bacterial species, particularly those causing disease. The consequences of these evolutionary events are increasing difficulties in preventing and treating bacterial infections. Antibiotic resistance can arise from mutations in the pre-existing genome of a bacterium or from the uptake of foreign DNA. Mutations readily occur and become fixed in the patient or animal treated with the antibiotic. The process is independent of the genetic reservoir in other species. The environment can provide a route for resistant bacteria to colonize or infect hosts. Environmental microorganisms have been a source for many novel antibiotic molecules, advancing drug development. Environmental surveillance of resistance, such as sewage monitoring, can provide insights into the regional resistance situation and historical antibiotic use. Sewage monitoring is particularly promising for large-scale surveillance, as it contains pooled faecal bacteria from large populations. It is less resource demanding than traditional clinical surveillance and can provide early warning for the emergence or spread of rare resistance factors. Studying resistance in the environment involves quantitative analyses of ARGs, resistant bacteria, and selective agents. The role of the environment as a source for new resistance factors is important to understand. Environmental analyses of antibiotics have advanced greatly, but accurately identifying and quantifying antibiotics at nanogram per litre levels in complex matrices remains challenging. The basis for environmental risk assessments is to compare exposure levels with effect levels, derived from simplified laboratory experiments. The ultimate concern with antibiotic pollution is the evolution of new, successful resistant genotypes in pathogens, causing difficult-to-treat infectionsAntibiotic resistance is a global health challenge, involving the transfer of bacteria and genes between humans, animals, and the environment. Although multiple barriers restrict the flow of bacteria and genes, pathogens recurrently acquire new resistance factors from other species, reducing our ability to prevent and treat bacterial infections. Evolutionary events leading to new resistance factors are rare and challenging to predict, but may have vast ramifications. Transmission events of already widespread resistant strains are common, quantifiable, and more predictable, but their consequences are limited. Quantifying pathways and identifying drivers and bottlenecks for environmental evolution and transmission of antibiotic resistance are key to understanding and managing the resistance crisis. The environment plays a role in resistance evolution, transmission, and as a reflection of the regional antibiotic resistance situation in the clinic. Current evidence, risk scenarios, surveillance methods, and potential drivers are discussed, along with actions to mitigate risks. Many bacterial species evolved the ability to tolerate antibiotics long before humans started mass-producing them. Isolated caves, permafrost cores, and other environments can provide insights into resistance mechanisms from the pre-antibiotic era. The competition for resources among microorganisms, including the natural production of secondary metabolites similar to antibiotics, is an important driver of resistance evolution. The introduction of antibiotics as clinical agents radically changed the preconditions for resistance evolution and spread, providing unprecedented selection pressures on human and animal microbiota and environments heavily polluted with antibiotics. This selection pressure has promoted the mobilization and horizontal transfer of antibiotic resistance genes (ARGs) to many bacterial species, particularly those causing disease. The consequences of these evolutionary events are increasing difficulties in preventing and treating bacterial infections. Antibiotic resistance can arise from mutations in the pre-existing genome of a bacterium or from the uptake of foreign DNA. Mutations readily occur and become fixed in the patient or animal treated with the antibiotic. The process is independent of the genetic reservoir in other species. The environment can provide a route for resistant bacteria to colonize or infect hosts. Environmental microorganisms have been a source for many novel antibiotic molecules, advancing drug development. Environmental surveillance of resistance, such as sewage monitoring, can provide insights into the regional resistance situation and historical antibiotic use. Sewage monitoring is particularly promising for large-scale surveillance, as it contains pooled faecal bacteria from large populations. It is less resource demanding than traditional clinical surveillance and can provide early warning for the emergence or spread of rare resistance factors. Studying resistance in the environment involves quantitative analyses of ARGs, resistant bacteria, and selective agents. The role of the environment as a source for new resistance factors is important to understand. Environmental analyses of antibiotics have advanced greatly, but accurately identifying and quantifying antibiotics at nanogram per litre levels in complex matrices remains challenging. The basis for environmental risk assessments is to compare exposure levels with effect levels, derived from simplified laboratory experiments. The ultimate concern with antibiotic pollution is the evolution of new, successful resistant genotypes in pathogens, causing difficult-to-treat infections