Internet is nowadays an integral part of our lives. However, excessive internet use, which is in many ways comparable to substance addictions and behavioral addictions, has become of growing interest in popular media, health policy and scientific research. Nevertheless, there is still considerable controversy with respect to diagnostic criteria and assessment questionnaires, and the diagnosis does not yet appear in any official diagnostic system such as the DSM-5 or ICD-10. Due to the lack of consistent diagnostic criteria for problematic internet use and both the use of different assessment questionnaires and classification systems, the reported prevalence rates vary significantly across studies. Thus, the comparison of study results is limited.In this review article a brief overview of the various diagnostic criteria and assessment questionnaires as well as the prevalence of problematic internet use (PIN) will be given. Furthermore, several usage-related and person-related risk factors of PIN will be discussed. With regards to the latter, the focus will be on both sociodemographic and psychiatric risk factors and on personality traits.