Built environments harbor a wide variety of microorganisms, and these microbial communities include both pathogens and strains carrying antibiotic resistance (AR) genes. One built environment that brings people together in our increasingly modern, urban world is public transit, so it's important to understand the relationships among the public transit environment, passengers, and microbes, including those in the air. Recently, researchers sequenced air microbiomes from public transit in 6 cities in North America, Europe, and Asia. City was the main factor associated with differences in public transit air microbiomes. Most AR genes came from human skin, soil, and wastewater and were found near mobile genetic elements including plasmids. Public transit air microbes were geographically specific, and the AR genes in public transit air came from passengers and the environment, including nearby surfaces. This study complements a previous large-scale study of microbiomes and AR genes from public transit surfaces and supports the development of public health risk management strategies that can help keep commuters safe.