Turkey has a great geothermal energy capacity due to Alpin Orogenesis. There are a lot of young magmatic intrusions and geothermal areas that is waiting be exploited in terms of shallow geothermal energy. Turkey's implementation of renewable energy is increasing in recent years due to the new energy policy targets. Shallow geothermal energy systems in Turkey have been increasing since 2007. Installed capacity of these systems is approximately 42,3 MW. Iller Bank Inc. Com. is a Development and Investment Bank servicing financial and technical support to municipalities in Turkey. With the purpose of setting an example of shallow geothermal application in official buildings for municipalities, a ground source heat pump system has been implemented at Iller Bank headquarters building in Istanbul-Atasehir in 2015. The building is located on metasandstone belonging to Paleozoic aged Kocatongel Formation. Heating and cooling demands of the building are approximately 1160 and 1817 kWh respectively. The ground source heat pump system was designed to supply some portion of this demand. 24 borehole heat exchangers with depths varying between 60 and 153 meters were installed. Thermal Response Test (TRT) was carried at two different borehole heat exchangers and effective ground thermal conductivity, undisturbed ground temperature, and resistivity were obtained. Thermal conductivity data from the TRT test showed significant differences due to ground water flow effect in one of the boreholes. In this paper, an overview of shallow geothermal systems in Turkey with a special focus on geological parameters will be given. As a case study, Iller Bank Atasehir Ground Source Heat Pump System will be analyzed.