Halitosis is defined as an unpleasant odor that emanates from the oral cavity with intra-oral and/or extra-oral origins. Fifty percent of people worldwide view themselves as having halitosis, with 90% of the etiology being intra-oral. Dental hygiene practitioners should be knowledgeable about the current classifications, diagnosis and treatment modalities to best meet the needs of patients either self-reporting or diagnosed with this problem. Classification of halitosis, assessment, diagnosis, intra-oral and systemic contributing factors, treatment, management and clinical application are discussed in this review.