Infectious diseases is a rapidly changing field in which new organisms emerge, previously identified organisms develop resistance to treatment, and infections that had previously almost disappeared become resurgent. These factors require rapid changes in therapeutic approaches, especially in the use of antimicrobial agents. This issue covers antibiotics in specific populations (children, the elderly, and patients with renal failure), antimicrobial resistance, and new drugs in several classes, including macrolides, fluoroquinolones, beta-lactam antibiotics, and agents for gram-positive infections.