The purpose of this thesis is to present different causes of tooth discoloration and to describe various techniques and materials used for tooth whitening and, in addition, to discuss the influence of tooth whitening on the hard and soft tissues of the oral cavity. Teeth whitening is a procedure that aims to restore the natural color of the teeth or lightens the color of the teeth by a few shades. Tooth discoloration can be caused by external, internal, or combined factors. External tooth discoloration is most commonly caused by the consumption of certain foods and beverages and precipitation of the pigments they contain on the tooth surface. Other causes include discoloration caused by tooth decay, old fillings, or plaque and calculus deposits. Most of these discolorations can be removed by prophylactic teeth cleaning at the dentist’s office, microabrasion, or at-home whitening. Internal discoloration can occur during tooth development or after the tooth has erupted. Internal factors can be divided into locally caused and systemically caused discoloration. The most common causes of locally caused discoloration are pulp necrosis and hemorrhage. Systemically caused discoloration occurs because of environmental or hereditary factors. There are several teeth-whitening techniques: in-office whitening, whitening under the supervision of the dentist, at-home whitening, and at-home whitening with over-the-counter products. The safest techniques are those performed by the dentist in the office or under his supervision. To minimize the possible risks, it is advisable to consult a dentist and reduce the use of over-the-counter products. Dentists should inform their patients about the possible negative effects and the realistic possibilities of teeth whitening.