This chapter provides an overview of outcome measures in neurology clinical trials, including developing a conceptual endpoint model, role and use of biomarkers, and considerations on how to select, use and interpret them in the context of early-stage clinical trial design. Early stage clinical trials (phase 1-2) often employ biomarker targets for proof of concept or therapeutic validation. Therapeutic development programs can be viewed as in the learn zone and confirm zone, with confirmation occurring in the phase 3 trial designed to test clinical efficacy against a standard or placebo. Structural imaging with MRI or computed tomography (CT) has been used as both an entry criteria into clinical trials and as an outcome measure. MRI has frequently been used as a measure of treatment response of multiple sclerosis (MS) patients. Researchers should define the role each endpoint is intended to play in the clinical trial.