Intra-abdominal infections (IAIs) represent the second leading cause of severe infection in intensive care units, preceded only by respiratory tract and followed by skin and soft tissue infections. Commonly referred to as peritonitis, they can occur either at home (community-acquired IAIs) or in hospital 48 h after admission (hospital-acquired IAIs). Additionally, they may occur in patients at risk of colonization/infection by multi-resistant germs, known as healthcare-associated IAIs. In an emergency department, the most common causes of IAIs are appendicitis, cholecystitis, diverticulitis and perforations of the gastrointestinal tract. In 15–20% of cases, they present initially in the form of septic shock. During the COVID-19 era, patients with abdominal pain and fever tended to present to emergency departments later, resulting in their intra-abdominal pathology reaching more critical conditions, often leading to septic shock requiring immediate resuscitation and potentially intensive care unit admission before definitive surgical therapy. Survival, in community- and hospital-acquired IAIs, as well as in healthcare-associated peritonitis, is dependent on the promptness of diagnosis and etiological treatment, both surgically (source control) and with antibiotics. In cases of persistent infection, re-laparotomy and/or open abdominal cavity treatments may be necessary to radically and definitively control the intra-abdominal sepsis.