Webinar 2.1 answers the questions: What is remote sensing? What is a satellite and how does it work? Which kind of sensor systems are available and what are their characteristics?. This webinar is part of the ESA EO4SD-Urban free webinar series on satellite-derived geospatial information for urban development. The webinars introduce the latest methodologies of obtaining geospatial information from satellite Earth Observation (EO) for urban development. The presenters are experts of the EO4SD-Urban consortium.