ABSTRACT As the global burden of ischemic stroke (IS) continues to rise due to population demographic shifts, new treatment approaches for stroke prevention are needed to address its public health burden. Survivors of a prior IS and individuals with atrial fibrillation (AF) are populations at highest risk for future stroke. Current medical therapies, such as aspirin and lipid lowering treatments, have limited benefit for secondary stroke prevention. While oral anticoagulation reduces the risk of IS in the setting of AF, the risk of major bleeding and nonadherence to therapy limits its effectiveness. Multiplexed proteomic profiling technologies have enabled the measurement of circulating proteins from large populations, and the integration of proteomics with genomic methods, have the potential to identify proteins that are etiologic factors of IS risk, and therefore potential targets for prevention. We propose to leverage previously collected plasma samples, genomic data, and longitudinal electronic medical record data from participants in the Heart and Vascular Health (HVH) Study. By measuring ~5,300 proteins in 659 IS cases and 972 AF cases using the Olink proteomics platform, we will evaluate the relationship between individual protein levels with the risk of future IS from up to 25 years of follow-up. For proteins significantly associated with IS risk, we will use genomic data from the study population and external cohorts to conduct Mendelian randomization and colocalization analyses to evaluate for evidence supporting potential causal relationships. Findings will then be replicated in participants of the UK biobank that have undergone Olink proteomic profiling. For key proteins associated with IS risk, we will develop targeted immunoassays to facilitate the translation of study findings to clinical settings. The rigorous and efficient approach described will accelerate the discovery of new etiologic factors and potential treatment targets for IS prevention.