There have been several recent changes that influence the management of intra-abdominal infections. These changes include important developments in antibiotic resistance such as increases in pneumococcal resistance, emergence of multi-drug-resistant enterococcal isolates, and decreasing sensitivity of anaerobes and gram-negative rods. In addition there are new antibiotics such as piperacillin/tazobactam, and new antibiotic dosing regimens such as single daily dosing of aminoglycosides. In this article, we will review the therapeutic approach to intra-abdominal infections with special emphasis on the various forms of peritonitis, cholecystitis, cholangitis, and diverticulitis. Several new concepts about the treatment of enterococcus, the management of bacterial and fungal peritonitis, and the prevention of spontaneous bacterial peritonitis will also be reviewed. Specific recommendations for the management of the different infections including antibiotic doses and costs will be provided. Finally the role of invasive procedures in the management of some of the infections will be explored.