Recent findings in research on avian chlamydiosis include an increase in the reported prevalence of Chlamydia (C.) psittaci in poultry flocks, detailed descriptions of molecular processes governing the course of infection in vivo, as well as the discovery of new chlamydial species. Here we review the major advances of the last 6 years. In particular, we suggest that the observed re-emergence of C. psittaci infections in domestic poultry are due to a reduction in the use of antibiotics and better diagnostic assays. Cellular and animal models have significantly contributed to improving our understanding of the pathogenesis, including the events leading to systemic disease. The elucidation of host–pathogen interactions revealed the efficiency of C. psittaci in proliferating and disseminating despite the action of pro-inflammatory mediators and other factors during host immune response. Finally, the recent introduction of C. avium and C. gallinacea sheds new light on the epidemiology and aetiopathology of avian chlamydiosis.