In this chapter, we introduce Internet- and mobile-based interventions (IMIs), present current evidence of different interventions, discuss limitations and its potential for implementation into clinical practice. We define IMIs as any digitally delivered intervention with the aim to change cognitive, emotional, and behavioral processes to support individual health goals, reduce symptoms and disorders, and enhance well-being. Several advantages are associated with IMIs as being flexible in time and location, scalable, potentially anonymous, and easily adaptable to other cultures and languages. An increasing body of literature in the past years supports the efficacy of IMIs, fewer studies focus on efficiency and implementation into practice. Nonetheless, robust evidence, mostly for cognitive-behavior-therapy-based interventions, has been reported in numerous meta-analyses. However, many studies are limited due to high dropout rates, short follow-up time points and do not include risk groups (e.g., participants with suicidal ideation). Studies focusing on children and adolescent are scarce—despite the technological affinity in this group. The potential of IMIs may still be fully exploited based on further pragmatic and real-life trials, cost-effectiveness studies and inclusion of key stakeholder and policymakers. IMIs undoubtedly have enormous potential to help a large population experiencing, at risk for, or recovering from mental disorders.