The term “Internet-use disorders” covers a range of different conditions including gaming and gambling disorder and problematic use of pornography, buying-shopping, and social networks. These conditions are often viewed and treated as addictive disorders. Although Internet-use disorders have been recognized as an internationally relevant public health issue, there is much controversy about this. The chapter addresses three topics, which remain highly debated. First, what defines a functional, regular behavior and what are potential criteria that differentiate between an excessive, a problematic, and a pathological use of specific Internet applications. Second, what defines impulsive, compulsive, and addictive behaviors in the context of Internet-use disorders, and what are the common and divergent characteristics that possibly explain the potential transition from addictive behaviors to compulsive behaviors? Third, what role does the smartphone or the use of one or more devices play and is the problematic use of smartphones automatically an Internet-use disorder? Possible implications for the future research and theory building are also discussed.