Data, and its timely delivery, present one of the major constraints in advancing hydrological sciences. Traditional monitoring techniques are time consuming, expensive, and discontinuous in space and time. Moreover, field observations are influenced by instrument degradation and human errors. While providing the foundation upon which much of our hydrological knowledge is based, new observational strategies are required to drive further understanding and insights. Recent advances in earth observation (EO) technologies via UAS represent a new frontier for hydrologic monitoring and process description. In the present chapter, we will introduce the potential offered by this technology for streamflow monitoring.