Halitosis or bad breath is an oral health condition characterized by unpleasant odors emanating consistently from the oral cavity. The origin of halitosis may be related both to systemic and oral conditions, but a large percentage of cases, about 85%, are generally related to an oral cause. Causes include certain foods, poor oral health care, improper cleaning of dentures, dry mouth, tobacco products and medical conditions. Oral causes are related to deep carious lesions, periodontal disease, oral infections, peri-implant disease, pericoronitis, mucosal ulcerations, impacted food or debris and, mainly, tongue coating. Thus, the aim of the present review was to describe the etiological factors, prevalence data and the therapeutic mechanical and chemical approaches related to halitosis. In general, halitosis most often results from the microbial degradation of oral organic substrates including volatile sulfur compounds (VSC). So far, there are few studies evaluating the prevalence of oral malodor in the world population. These studies reported rates ranging from 22% to more than 50%. The mechanical and chemical treatment of halitosis has been addressed by several studies in the past four decades. Many authors agree that the solution of halitosis problems must include the reduction of the intraoral bacterial load and/or the conversion of VSC to nonvolatile substrates. This could be achieved by therapy procedures that reduce the amount of microorganisms and substrates, especially on the tongue.