As part of the Tigecycline Evaluation and Surveillance Trial (TEST), bacterial isolates were collected consecutively from centers globally between 2004 and 2009. MICs were determined locally using Clinical and Laboratory Standards Institute broth microdilution methodology. A total of 3114 anaerobic and 99,256 aerobic isolates were included in this study. The most active agents against Gram-negative anaerobes were metronidazole and meropenem (resistance ranges 0.0-0.5% and 0.0-0.9%, respectively); piperacillin-tazobactam was also active (resistance range 0.5-9.4%). Among Gram-positive anaerobes, resistance rates were lowest for meropenem, piperacillin-tazobactam, and metronidazole (ranges 0.0-0.5%, 0.0-1.8%, and 0.0-3.2% respectively). Tigecycline MIC(90) values for anaerobes ranged from 0.12 to 2 μg/mL. The most active antimicrobial agent against Gram-negative aerobes (excluding Pseudomonas aeruginosa) was tigecycline, with resistance ranging from <0.01% to 1.4%. Resistance was also low for imipenem (0.3-9.4%) and meropenem (0.7-15.1%). Extended-spectrum beta-lactamases were produced by 12.2% and 19.7% of E. coli and K. pneumoniae isolates, respectively.