Bruxism is a repetitive jaw-muscle activity characterized by clenching or grinding of the teeth. Depending on the time the activity occurs, we differentiate between “awake bruxism” and “sleep bruxism”. “Sleep” or “nocturnal bruxism” is an involuntary jaw-muscle activity classified as a sleep disorder. In contrast, “awake” or “diurnal bruxism” is defined as a conscious clenching of jaws. Bruxism negatively affects patient's quality of life and is often associated with other disorders such as insomnia or emotional stress. Early diagnosis of bruxism is advantageous so that a dentist can devise a treatment plan according to specific activities related to patient's muscles, the degree of bruxism and the time it takes place. A diagnosis of bruxism is usually made clinically and is mainly based on the presence of typical signs and symptoms, but we also use complementary methods, such as electromyography and polysomnography, to measure bruxism activity. Signs that could indicate bruxism are tooth wear, tooth fractures, tooth mobility, pulp necrosis, traumatic ulcers, hypertrophy of masticatory muscles, linea alba and teeth marks on the tongue. Due to its multifactorial etiology, the therapy of bruxism should be based on behavioral, oro-dental and pharmacological approach, although neither of these approaches can successfully treat bruxism.