The Urban Heat Island (UHI) effect occurs when the temperature in an urban area is higher than the temperature in a rural area. UHIs are generally monitored using remote sensing techniques such as satellite imagery or using temperature sensors deployed in a metropolitan area. In this chapter, a newly proposed methodology to monitor the UHI intensity from Global Navigation Satellite Systems (GNSS) data is described. As the GNSS signal travels from the satellite to the receiver it propagates through the troposphere the travelling signal is delayed by the troposphere. The tropospheric delay is proportional to environmental variables. The tropospheric delay in zenith direction (ZTD) is estimated as part of the Precise Point Positioning (PPP) technique. Therefore, this chapter shows how to process GNSS data to obtain ZTD and how to obtain temperature at an urban and a rural site simultaneously from the ZTD. The advantages of using GNSS data is its availability and many GNSS networks have been deployed in different cities so no need to deploy sensor networks. Furthermore, GNSS signal is less affected by bad weather conditions than satellite imagery.