Background <p>Despite grief being a universal experience, current understanding of the trajectory and predictive factors of the new condition, Prolonged Grief Disorder (PGD), mostly arises from studies conducted in Europe and North America. Research suggests cultural variations in how grief develops across time. This study aims to longitudinally compare PGD growth patterns across Swiss, Vietnamese, and Rwandan bereaved individuals.</p> Methods <p>Due to grief’s wave-like nature, experience sampling methods (ESM) enables a fine-grained temporal analysis of grief manifestation. A total of 100 bereaved individuals from each country who lost a loved one in the last 3 years will complete a 2-week ESM assessment app (mPath) every 3 months for 6 months (Viet Nam and Rwanda) or 18 months (Switzerland). The app sends daily reminders to complete a questionnaire about PGD symptoms and daily life context. Participants will also complete a baseline mental health assessment before each ESM period. The primary outcomes are symptom variability and chronicity, while secondary outcomes include culturally specific predictive factors of prolonged grief symptoms (e.g., mourning rituals). Acceptability and feasibility of daily assessment will also be assessed. The method and specific ESM items have been developed and tested through cognitive interviews with bereaved individuals from each cultural group to ensure cultural acceptability.</p> Discussion <p>The current study is the first to longitudinally explore potential cultural variations in grief trajectories across Swiss, Vietnamese, and Rwandan bereaved individuals. This study has significant potential to contribute to more nuanced, culturally informed, and technologically integrated approaches to bereavement care.</p>