ABSTRACT The impact of genetic testing for disease prevention hinges on cascade screening, the process of systematically identifying and testing relatives in families with a genetic condition. Lynch syndrome is a genetic condition that confers an increased lifetime risk of cancer. Unfortunately, only half of first-degree family members with Lynch syndrome receive cascade screening, representing a missed opportunity in cancer prevention. Let's Talk is a novel intervention to promote and support cascade screening in families with Lynch syndrome. Developed using intervention mapping, a 6-step, stakeholder-engaged methodology for developing theory-based interventions, the workbook intervention addresses barriers to cascade screening through information chunking, guided practice, planning coping responses, and gain frame messaging for patients, their provider and family. Preliminary data have demonstrated that the content of Let's Talk, in a paper-based format, is acceptable to patients with Lynch syndrome, and all patients reported that they would recommend its use to someone recently diagnosed with Lynch syndrome. In addition, all patients in our usability study endorsed the development of an interactive, online version, which could improve dissemination, given changes in genetic counseling workflows due to COVID-19, and could facilitate ongoing patient support through follow- up messaging. Thus, the overall objective of this project is to (1) adapt and refine an interactive online format for Let's Talk based on patient preferences and user feedback, and (2) pilot test Let's Talk to assess its feasibility by measuring implementation (primary) and effectiveness outcomes. The expected outcomes of this project will move the field forward in tackling challenges associated with cascade screening in Lynch syndrome and other hereditary conditions. This work will provide foundational data for a future R01 application to test the effectiveness and implementation of Let's Talk for increasing cascade screening uptake and identification of relatives with Lynch syndrome across diverse care settings.