This thesis aimed to explore the potential use of technology, namely websites and smartphone applications â(apps)â, to deliver psychological interventions for people who experience severe mental health problems (SMI). In particular, it sought to understand the views of mental health care staff and service users towards the use of digital health interventions (DHIs) for self-management, identify what service users want and need from a DHI, explore how people currently use the Internet and smartphones to self-manage their mental health and investigate the impact of specific technology use on symptoms associated with SMI. To achieve this, a multi-methods approach was taken, including reviewing evidence of the existing literature, qualitative interviews and focus groups, circulating a hashtag on the social media website Twitter, and experience sampling methodology. Chapter 1 provides an overview of the literature and rationale for the thesis and chapter 2 describes the methodology employed. Chapter 3 (study 1) describes a systematic review of the acceptability of DHIs for the self-management of SMI. This review highlighted that acceptability should be identified prior to or without an individual receiving an intervention (hypothetical acceptability) and after intervention delivery (actual acceptability) and hypothetical acceptability tended to be lower than actual acceptability. Chapter 4 (study 2, N=18) outlines a qualitative exploration of service user views towards the hypothetical acceptability of DHIs for self-management and ideas for future developments. Five main themes were generated from thematic analysis of the data: 1) DHIs could be empowering tools that instigate shared understanding and decision-making; 2) DHIs may widen the current divides in society; 3) service users are uncertain about who may have access to data held on digital devices and how data may be used; 4) DHIs should not be used replace other support options; and 5) DHIs should be positive, fun, practical and interactive. Chapter 5 (study 3, N=20) describes findings from focus groups with mental health care staff about the hypothetical acceptability of DHIs for SMI. Four main themes were generated from thematic analysis of the data: 1) staff hold conflicting views about the pros and cons of using DHIs; 2) DHIs could increase access to support options, bur may perpetuate the digital divide; 3) DHIs impact on staff roles and responsibilities; and 4) DHIs should be used to enhance, not replace, face-to-face support. Chapter 6 (study 4, N=90) presents the findings from a novel study that circulated the hashtag #WhyWeTweetMH on the social media website Twitter. Thematic analysis of the tweets led to the creation of four main themes, which described that individuals tweeted about mental health: 1) to feel part of a community; 2) to combat stigma and raise awareness; 3) because Twitter is a safe space for expression; and 4) because it is an empowering coping mechanism. Finally, chapter 7 (N=50) presents findings from study 5, which used experience sampling methodology to explore the relationship between social media use and behaviours and mood, self-esteem and paranoia. Social media use predicted low mood, whilst positing emotional disclosures on social media websites predicted decreases in mood and increases in paranoia. The findings from the overall thesis form six main themes, which are presented in chapter 8: DHIs have the potential to empower individuals with SMI; DHIs should include strengths-based and recovery-oriented content; DHIs should include remote support options; findings support the use of the CHIME framework in DHI design; digital exclusion may prevent some people from being able to access DHIs; and staff and service users fear that DHIs will be used to replace face-to-face intervention options.