Ever since the invention of the World Wide Web in 1989 [1], the Internet has dramatically reshaped all walks of life. It has also expanded the spectrum of Internet-related disorders in the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) and the eleventh revision of the International Classification of Disease (ICD-11) [2,3]. Research on Internet-related addictions can be dated back to 1996 when problems associated with excessive Internet use in general, such as Internet Addiction (IA), were studied [4]; IA has been found to cause various physical problems and psychopathology among adolescents and adults [5]. There are different types of Internet-related addiction [6,7], such as Internet gaming disorder (IGD), problematic mobile phone use (PMPU), social networking addiction (SNA), and Internet gambling. These subtypes have common (e.g., heightened impulsivity) and specific (e.g., maladaptive expectancies) characteristics [8]. This Special Issue has gathered 15 papers that have looked into important topics of research on various types of Internet-related addiction.First, as the cornerstone of studying Internet-related addictions, it is essential to improve the assessment accuracy for a specific addiction. Ko et al. [9] adapted a gaming version of the commonly used Chen Internet Addiction Scale, the CIAS-G, to assess the DSM-5 IGD based upon data of 69 clinically diagnosed IGD cases, 69 regular Internet gamers, and 69 healthy Internet gamers in Taiwan. The screening (≥68), diagnostic (≥72), and prevalence-estimate (≥76) cutoff points were proposed to identify probable IGD for different clinical and epidemiological utility. Future studies may further validate this tool and compare it with existing tools, especially those based on the ICD-11 criteria. While many studies investigated the cognitions of Internet-related addictions and associated impacts [10], there is a dearth of studies validating measurement tools to assess such cognitions in a systematic way. Yu et al. [11] validated and further revised the Internet Gaming Cognition Scale, which was originally based on a systematic review of cognitive factors of IGD, among 755 Chinese junior high school students. The authors identified three types of maladaptive Internet gaming cognitions, including perceived rewards of Internet gaming, perceived urges for playing Internet games, and perceived unwillingness to stop playing without completion of gaming tasks. These maladaptive cognitions were found to be significantly associated with heightened impulsivity, impaired self-control, increased gaming time, and higher risk for IGD. This validation study strengthens research on relationships between cognitions and IGD. Relatedly, Chia et al. [12] conducted a scoping review of cognitive bias in IA and IGD. Of the six identified studies, five demonstrated existence of cognitive biases among individuals with IA/IGD; one study demonstrated effectiveness of bias modification for IGD. Cognitive bias and bias modifications related to IA/IGD are im...