Pathogenic bacteria dispersed into the outdoor air from natural events or human activity are an important concern affecting public health, agriculture, ecological health and international security. Recent studies in atmospheric microbiology have contributed to our ability to detect bacterial pathogens in air samples, increased our knowledge of the spatial and temporal dispersal of aerosolized bacteria and furthered our understanding of the natural bacterial diversity and composition of air. Significant questions remain about bacterial dispersal and diversity in outdoor air that will benefit from continued technological advances. These include determining spatial and temporal patterns of aerosol dispersal, identifying the links between detection, concentration and viability of bacterial pathogens and disease incidence, and documenting the composition and regional movement of bacterial species in air.