The purpose of this Ph.D. was to research and design an online educational application about cybersafety for young people with intellectual disability (PwID), employing a user-centred design (UCD) methodology. PwID are twice as likely to be victims of cyber victimisation as their peers. The context for this Ph.D. study is the increasing demand from stakeholders for interactive educational materials about cybersafety for vulnerable PwID, with a wider inclusive agenda to include PwID in their design. The focus of this study was primarily on PwID engagement in the UCD process, as opposed to investigating the effectiveness of the learning from an instructional perspective. The digital divide theoretical framework as it applies to PwID and the importance of digital literacy including cybersafety for this vulnerable user group are discussed as well as the lack of suitably designed educational resources. User-centred, participatory and codesign approaches are explored as are recommendations for interface design for PwID. The literature review culminates with a discussion of the dimensions of user experience i.e., usability, engagement and aesthetics in relation to PwID. The thesis then describes three phases of UCD research, during which four qualitative datasets were collected and analysed using thematic analysis. Three key contributions resulted from this study: firstly, a wide range of insights related to cybersafety for PwID, such as their vulnerability to celebrity catfishing and how risk exposure can result in positive personal growth. Secondly, a usable educational prototype application called CyberSafe was co-designed and finally, a toolkit of best practice for UCD for PwID under four headings (Research, Methods, Tools and Content Design) recommended the use of step-by-step videos, interactive video and interactive exercises to enhance accessibility, engagement and usability for PwID. The final CyberSafe prototype is a hybrid web application, which can run on mobile, tablet or desktop as an educational tool.