Objective The high level of stress associated with caring for others with medical conditions has been recognized for some time. Reducing caregiver stress can improve caregiver quality of life as well as improve the care they provide to loved ones. This systematic review assesses the effectiveness of internet-based interventions to decrease caregiver stress.Materials and methods A comprehensive literature search of Ovid MEDLINE (1946–2013), Embase (1988–2013), PsycINFO (1987–2013), and CINAHL was conducted using terms related to caregiver and internet-based interventions. Internet-based interventions involving informal caregivers in an open-label or randomized controlled trial setting were included. A pair of raters independently reviewed all published abstracts. Data regarding participants, interventions, and outcomes were extracted and, for randomized trials, methodology quality was also reviewed.Results Eight open-label trials met the review criteria: three showed positive benefit in reducing caregiver stress, four were partially positive (some outcomes positive, others negative), and one was a negative study. Sixteen randomized trials met the review criteria: six showed positive benefit, five were partially positive, and five were negative. There were no clear patterns as to the variables (such as study duration and complexity of intervention) associated with better outcomes, although earlier studies typically had more negative outcomes.Discussion Internet-based interventions were mostly effective in reducing aspects of caregiver stress and improving their well-being. Further studies to assess outcomes for caregivers and their recipients’ health, different technology delivery methods, and the cost of such interventions are needed.