Multiple Sclerosis (MS) is a chronic inflammatory disease of the central nervous system (CNS) causing focal lesions of demyelination and diffuse neurodegeneration in the grey and white matter of the brain and spinal cord, leading to physical and cognitive disability. The scientific community and patients are in need for new and more reliable biomarkers, especially biomarkers of disease progression in order to adapt therapeutic approaches on an individual level. Digital biomarkers have the potential to fill this gap allowing for quasi-continuous measures that might be more informative than episodically collected conventional data concerning the impact of the disease on activities of daily living. Using app-based challenges, continuous monitoring and surveys the Investigators aim to obtain data that can be used as digital biomarkers (DB). These digital biomarkers will provide more granular and precise assessments, thus complementing traditional diagnostic measures and techniques. After a first feasibility study (ClinicalTrials.gov: NCT04413032) a number of digital biomarkers have been identified as reliable, reproducible and meaningful to PwMS and are therefore being validated in a bigger cohort of PwMS with a longer follow-up within this validation study 1. Those digital biomarkers will be compared to state-of-the-Art clinical, imaging and body fluid assessment.