Clinical susceptibility breakpoints against Enterobacteriaceae and Pseudomonas aeruginosa for the ceftazidime-avibactam dosage regimen of 2,000/500 mg every 8 h (q8h) by 2-h intravenous infusion (adjusted for renal function) have been established by the FDA, CLSI, and EUCAST as susceptible (MIC, ≤8 mg/liter) and resistant (MIC, >8 mg/liter). The key supportive data from pharmacokinetic/pharmacodynamic analyses, in vitro surveillance, including molecular understanding of relevant resistance mechanisms, and efficacy in regulatory clinical trials are collated and analyzed here.