Despite plenty of research on the topic of smartphone addiction, or problematic smartphone use, there is considerable disagreement on how it is defined. This chapter explores the main issues concerning how smartphone addiction is conceptualised, specifically focusing on: (a) whether smartphone use meets accepted criteria for an addiction, (b) whether the device or the content on it is the focus of the proposed disorder, (c) the relationship between smartphone addiction and internet addiction, and (d) the relationship between smartphone addiction and other technology use constructs. Each issue raises implications for how smartphone addiction could be conceptualised. Alongside these issues, we introduce key theories used to explain smartphone addiction.