Since the advent of the internet, convictions for the possession, display, trading and distribution of child sexual exploitation material (CSEM) have risen steadily. Professionals working in sex offender assessment and treatment have seen an influx in individuals who engage in this type of child sexual abuse without any direct contact with the victim. Despite an increase in recent research activities, there is still a lack of knowledge regarding this “new type” of sex offenders, in terms of appropriate assessment, treatment and management strategies. A comprehensive review was undertaken, establishing the knowledge basis regarding CSEM offending and the offenders who engage in it. The identified differences between CSEM offenders (CSEMOs) and contact sex offenders (CSOs) and the nature of their offending led to the development of a theoretical model of CSEM offending, suggesting a classification of CSEM users on three dimensions: CSEM offending with or without direct sexual contact to a minor (fantasy-driven versus contact-driven offending), the individual’s motivation to offend, and the level of networking with other offenders. The question of risk of reoffending in CSEMOs, especially concerning cross-over to contact sex offending with a minor, was examined in terms of actual reoffending data and in the context of behavioural consequences resulting from general pornography consumption. The findings further confirmed the value of the two-fold distinction of CSEMOs, with contact-driven offenders presenting higher risk of direct sex offending based on a greater inclination for sexual violence. A review of existing risk assessment tools and established risk factors for sexual reoffending pointed to the value of structured professional guidelines when assessing CSEM offenders. Sixty-eight offenders were assessed via an anonymous computer survey including a variety of clinical and risk-related variables; the sample included 22 CSEMOs, 29 CSOs, and 17 offenders with both offence types (mixed offenders, MOs). The findings confirmed differing profiles between CSEM users and CSOs, most notably in the high emotional, time-related and financial cost involved in CSEMOs’ internet behaviour and MOs’ apparent disregard for their emotional ties to others. As a heterogeneous nature of CSEM users became apparent, numerical and graphical methods were employed to identify subgroups of CSEM users: Contact-driven Users (n = 15), Fantasy-driven Users (n = 12), and three smaller subgroups (each n = 2): Users with a preference for material with extreme content (Extreme Material Users), users who enacted high caution in their CSEM offending (Cautious Users), and users with high social connectedness (Social Users). While the focus of Contact-driven Users was pointed to direct sexual contact with minors, Fantasy-driven Users showed higher involvement in their CSEM usage, for example regarding their social or emotional investment online. The spatial representation of participants identified three dimensions as crucial in the classification of these subgroups: direct sexual contact with a minor, possession of fantasy-generating material, and social contact with other users with a sexual interest in minors. Exploring the subgroups’ profile on these variables and on conventional predictors of sex offending led to the development of an empirical model of CSEM users, differentiating a contact-driven pathway (Cautious Users, Contact-driven Users) from a fantasy-driven pathway (Extreme Material Users, Fantasy-driven Users, and Social Users), with offenders on the contact-driven pathway appearing more similar to CSOs. The theoretical and empirical models were then combined into an Integrated Model for the Classification, Assessment, and Treatment of CSEM Users (IMCAT-CU), leading to the development of structured professional guidelines for their assessment and risk evaluation according to the five prototypes of CSEM offending.