Sleep bruxism (SB) consists of involuntary episodic and repetitive jaw muscle activity characterized by occasional tooth grinding or jaw clenching during sleep. Prevalence decreases from 20% to 14% in childhood to 8% to 3% in adulthood. Although the causes and mechanisms of idiopathic primary SB are unknown, putative candidates include psychologic risk factors (eg, anxiety, stress due to life events, hypervigilance) and sleep physiologic reactivity (eg, sleep arousals with autonomic activity, breathing events). Although certain neurotransmitters (serotonin, dopamine, noradrenalin, histamine) have been proposed to play an indirect role in SB, their exact contribution to rhythmic masticatory muscle activity (RMMA) (the electromyography marker of SB) genesis remains undetermined. No specific gene is associated with SB; familial environmental influence plays a significant role. To date, no single explanation can account for the SB mechanism. Secondary SB with sleep comorbidities that should be clinically assessed are insomnia, periodic limb movements during sleep, sleep-disordered breathing (eg, apnea-hypopnea), gastroesophageal reflux disease, and neurologic disorders (eg, sleep epilepsy, rapid eye movement behavior disorder). SB is currently quantified by scoring RMMA recordings in parallel with brain, respiratory, and heart activity recordings in a sleep laboratory or home setting. RMMA confirmation with audio-video recordings is recommended for better diagnostic accuracy in the presence of neurologic conditions. Management strategies (diagnostic tests, treatment) should be tailored to the patient's phenotype and comorbidities. In the presence of sleep-disordered breathing, a mandibular advancement appliance or CPAP treatment is preferred over single occlusal splint therapy on the upper jaw.