Atherosclerosis is the main pathological mechanism causing myocardial infarction and ischemic stroke. Evidence has mounted about the association between the gut microbiota and cardiovascular disease, but whether the associations are causal is largely unknown. For optimal prevention and treatment of cardiovascular disease, there is an urgent need to determine whether there are any true effects that might be targeted by interventions. The overall goal of this project is to assess causality between gut microbiota and atherosclerotic disease and to provide easily accessible biomarkers for an atherosclerosis-enhancing gut microbiota. To this end, the research program has three main objectives: 1.) Identification of gut microbiota characteristics associated with atherosclerosis measured by coronary computed tomography angiography and high-resolution carotid ultrasound in a population-based sample of 10,000 individuals and through prospective follow-up for myocardial infarction and ischemic stroke. The microbiota will be characterized by next-generation sequencing techniques in faecal samples. 2.) Identification of plasma biomarkers associated with an atherosclerosis- enhancing microbiota using comprehensive metabolomics profiling of 800 named metabolites in plasma from 800 individuals with replication in additional 800 individuals 3.) Clarification of the causal effects of gut microbiota characteristics on atherosclerosis, myocardial infarction and stroke by development of novel genetic instruments and applying Mendelian Randomization analysis