Importance: Olfactory dysfunction affects approximately 20% of the general adult population. It is associated with reduced quality of life and important health care outcomes such as neurodegeneration and death. The accurate diagnosis of olfactory dysfunction is therefore important to quantify impairment, the effect of intervention, and residual disability. This review summarizes the current evidence on the diagnosis and management of olfactory dysfunction. Observations: Olfactory dysfunction can be quantitative and/or qualitative. Despite numerous underlying pathophysiological causes, approximately two-Thirds of cases are due to sinonasal disease or postinfectious or posttraumatic dysfunction. All patients should undergo assessment with a thorough clinical history and examination (including nasoendoscopy) followed by subjective olfactory assessment and some form of validated psychophysical test. Psychophysical tests should include assessment of odor threshold and/or odor discrimination or identification, although multicomponent testing has diagnostic advantages. Imaging of the olfactory tract and brain is indicated for a high index of suspicion for intracranial pathology. Treatment with olfactory training may benefit patients with nonsinonasal dysfunction. Treatment with medications such as phosphodiesterase inhibitors or intranasal sodium citrate require further research, as do nonchronic rhinosinusitis-related surgical procedures. Conclusions and Relevance: This multifactorial assessment and patient olfactory training may improve the accuracy and reliability with which olfactory dysfunction is diagnosed and monitored.