Bad breath (halitosis) is an important social complaint. In most cases (≥90%), the cause of halitosis can be found within the oral cavity. Under this circumstance, the term oral malodor applies. It affects both healthy and periodontally diseased individuals. Oral malodor is mainly caused by a microbial degradation of both sulfur-containing and nonsulfur-containing amino acids into volatile, bad-smelling gases. Anaerobic gram-negative bacteria, the same species that have been linked to periodontal diseases, are especially involved in this process, explaining why clinicians often associate oral malodor with periodontitis. Some volatile organic compounds render patients more susceptible to periodontitis and this supports the malodor–periodontitis link. This review investigates the interaction between oral malodor and periodontal diseases. Pro and con arguments regarding the mechanisms of halitosis and clinical implications will be presented. In general, however, the impact of tongue coatings has been found to be the dominant factor, besides gingivitis and periodontitis. The last part of this review discusses the treatment of bad breath, with different options.