The extended-spectrum β-lactamases have evolved owing to the extensive use of the oxyimino-cephalosporins, and have greatly reduced the treatment options for serious infections. Acinetobacter baumannii is becoming an increasingly important multiresistant nosocomial pathogen due to the carriage of class D OXA-type β-lactamases. The OXA-23-like, OXA-40-like and OXA-58-like β-lactamases confer carbapenem resistance and are increasingly being found in association with a diversity of mobile genetic elements. High prevalence of OXA-40-like enzymes on the Iberian Peninsula, OXA-58-like enzymes across Europe and very high prevalence of OXA-23-like enzymes in South America and Asia are of concern. The intrinsic OXA-51-like enzymes of A. baumannii may confer carbapenem resistance when overexpressed, and form a large enzyme family. Similar patterns are beginning to be seen for the OXA-type β-lactamases, which were previously seen in the emergence of the extended-spectrum β-lactamases, the continuation of which would pose a grave threat to the antibiotic era.