It is impossible to imagine the world today without the use of the Internet. Due to the increasing availability of the Internet and other predisposing factors, a relatively new addiction is on the rise globally – Internet addiction. Internet addiction primarily falls under behavioral addictions meaning it excludes the consumption of psychoactive substances. However, some authors define it as an impulse control disorder or a compulsive disorder. Various authors offer different definitions of Internet addiction but they all share the common characteristic of the inability to control Internet use. There is disagreement among experts about the various types of Internet addiction and there are also several models that explain the emergence of this phenomenon. In professional literature different terms are used for Internet addiction, such as problematic Internet use, pathological Internet use, compulsive Internet use, and Internet addiction disorder, among others. Internet addiction is not recognized as an official diagnosis in the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) or in the 10th edition of the International Classification of Diseases and Related Health Problems (ICD-10), which complicates diagnosis, measurement of prevalence, planning of interventions, and preventive programs. However, video game addiction is included in the latest edition of the International Classification of Diseases (ICD-11) which implies a recognition of technological addictions. Internet addiction appears alongside a range of other comorbidities such as depression, ADHD, anxiety, bipolar disorder but there is the question of causality – does Internet addiction cause other mental disorders or do mental disorders lead to Internet addiction. Internet addiction causes numerous consequences for mental and physical health making it essential to offer effective treatment modalities primarily psychological, pharmacological and combined approaches. Most importante is to educate the population especially the most vulnerable group – adolescents and young adults – to recognize symptoms in time and to start treatment promptly. The aim of this paper is to provide a literature review on the topic of Internet addiction touching on several aspects such as terminology, definition, diagnostics, consequences, treatment and prevention.