Joined the 1 GW installed capacity club in 2017, Turkey has undeniable production and potential for geothermal energy, ranking top 5 worldwide. Harnessing geothermal energy has many challenges, from planning to commercial phases. This study features the challenges, experiences and latest advances in drilling fluids utilized in geothermal well construction process in Turkey; focusing to provide a comprehensive information about drilling fluids systems and their design principles in geothermal wells in Turkey.GEOS act as a major player in Turkish geothermal drilling industry; providing drilling and completion fluids, solids control equipment and waste management services; having drilled more than 250 deep geothermal wells in utmost challenging downhole environments of Turkish geothermal fields with major operators. Drilling geothermal wells comes along with several challenges. Most important of which could be high temperatures, relatively high pressures and some of the wells having tough lithologies to drill through. Providing wellbore stability across dispersive shales or pressurized ophiolitic formation requires special attention in planning and execution phases. Another special attention has been given to minimize formation damage in reservoir intervals of geothermal wells. Therefore, different options of reservoir drilling fluids are presented and discussed in detail. Drilling fluids systems used in geothermal wells have evolved over the last decade and tailored to suit the challenges to be faced, not only in top hole and intermediate intervals, but also in reservoir intervals. Main objective of this paper is to share the knowledge and experience gained during the learning curve over the years; extensive laboratory studies and field case studies for geothermal well drilling fluids in Turkey are presented.