Irritable bowel syndrome is a common and recurrent disease occurring at all geographical latitudes. The prevalence in the northern hemisphere is estimated at 11%, with more women affected than men (2:1). The symptoms usually develop in the third or fourth decade of life. The aetiology of the disease is complex and not fully explained. Genetic factors, gastrointestinal motor dysfunction, visceral hypersensitivity, psychological stress and intestinal infections are believed to contribute to the etiopathogenesis. Irritable bowel syndrome reduces life quality and work productivity as well as is a considerable financial burden for both health care system and patients themselves. Despite its arduous course, it does not lead to the development of a serious disease with excessive mortality. Irritable bowel syndrome is characterised by recurrent abdominal pain related to defecation, change in bowel habits and/or stool consistency. The diagnosis of irritable bowel syndrome is currently based on the Rome IV diagnostic criteria published in 2016. These criteria are the latest update of the diagnostic criteria for gastrointestinal functional disorders now defined as disorders of gut–brain interaction. Irritable bowel syndrome is currently defined as abdominal pain that has occurred on average at least 1 day per week during the previous 3 months, which meets at least 2 of 3 criteria: 1) is related to bowel movement, 2) is related to a change in stool frequency, 3) is related to a change in stool consistency. The paper presents the main changes introduced in the Rome IV criteria, their rationale and implications for clinical practice.