This thesis has been written about the effects of smoking on the oral cavity. It includes some information on the general effects of smoking on the body: immunomodulatory and carcinogenic pathomechanisms are briefly explained. It also discusses the link between smoking and several oral conditions/diseases: periodontal disease, xerostomia, caries, cancers and premalignant lesions. The relevance of dental practitioners knowing a patient's smoking habits becomes clear throughout the thesis. This is due to smoking leading to an increase of prevalence of many oral diseases and the benefits of smoking cessation interventions during dental appointments.