The GriefDiff study is a randomized controlled trial evaluating a differentiated, community-based model of grief support for older adults. It compares three intervention levels-Information and Grief Literacy (IGLiteracy), Individual Self-Help Program (ISelfHP), and Moderated Self-Help Groups (MSHGroups)-to assess their effectiveness in reducing prolonged grief and psychological distress. Participants are screened for risk of Prolonged Grief Disorder and relational needs, then randomized to matched or non-matched interventions. Outcomes are measured at baseline, post-intervention (3 months), and follow-up (6 months), focusing primarily on prolonged grief symptoms and secondarily on depression, anxiety, stress, attachment, social support, and traumatic stress. The study aims to provide evidence for a cost-effective, scalable, and preventive public health model of bereavement care.