In order to promote the development of geothermal energy production from deep resources, cost effective solutions to increase the drilling performance have to be developed. Currently, the drilling costs account for up to 70% of the total investment for a deep geothermal project. Besides the different attempts to intensify the conventional drilling process, several emerging technologies are currently investigated by researchers around the world. One of these alternative technologies is the spallation technology, which is based on the effect of hard, crystalline rocks disintegrating into small fragments, if rapidly heated by a hot fluid jet. Thermal spallation drilling has the benefits of high penetration rates in hard rock formations, an efficient energy transport to the bit and reduced wear-rates. Previous research has indicated that these benefits could lead to a decrease of the drilling costs and therewith to a boost in the development of geothermal energy production from deep resources. Even though, thermal spallation drilling is used since decades for hard rock excavation, no deep bore hole has been drilled with the technology, as some important questions remain still open. The presented thesis aims at closing these open questions and to demonstrate the application possibilities of thermal spallation drilling and its operational readiness. Thereby, the deeper understanding of the physics of the spallation process and their transfer to practical applications shall be an essential building block for the discussion about this technology. In order to assess the viability and the economical aspects of thermal spallation drilling without extensive full-scale experiments, a comprehensive modeling approach is required. This model has to be capable to predict the operating conditions of a thermal spallation drill head, which are required to drill a certain formation with a desired drilling velocity without any further calibration measurements. Only if such a model is available, an economical assessment of the technology, evaluating if thermal spallation drilling can reduce the drilling costs, is possible. Therefore, two interlinked models are presented. The first model is based on a linear fracture mechanical consideration and can be used to predict the operating conditions, which are required to drill a certain rock formation and to assess the spallability of rock formations. The second model is based on an analytical heat transfer approach and predicts the drilling velocity, which can be reached by using thermal spallation drilling, as a function of the drill head operating conditions and the prevailing rock formation. This model can also be used to design spallation drill heads with respect to the applied combustion reaction and the required jet velocities. After the introduction of the spallation model, opportunities and challenges for thermal spallation drilling in deep drilling operations are discussed. A case study is conducted, comparing the investments, which are required to drill an exemplary well with thermal spallation drilling and with conventional drilling methods. Therewith, it gives a perspective on the financial aspects of thermal spallation projects in great depths. Thereafter, the differences between laboratory experiments and drilling operations in deep bore holes are discussed. Finally, supply solutions for the reactive fluids, required to establish the flame-jet, are assessed and their applicability is investigated. The chapter closes with a recommendation of the application possibilities of thermal spallation drilling and with a discussion, which limitations restrict the use of this technology. In order so solve the revealed issues of stand-alone thermal spallation drilling, a combination of spallation drilling and mechanical drilling is investigated. The principles of such a combined drilling method are assessed together with its potential benefits. In order to demonstrate the general feasibility of a thermo-mechanical drilling system, a first feasibility study by means of thermal treatments is conducted and implementation possibilities are discussed. The applicability of this hybrid system is demonstrated in a full-scale hybrid drilling system, designed in cooperation with the Geothermal Center in Bochum (GZB). This system has a length of about 11m and a diameter of 140mm. The design aspects of the system are discussed and the drill head is tested in an laboratory environment. With these experiments, the feasibility of a combined system is shown and its potential impact on the enhancement of geothermal energy production is revealed. Additionally, a novel process is developed in this thesis, which utilizes thermal spallation drilling to enhance and enlarge the bore hole diameter in the reservoir section of the well. Thermal bore hole enlargement aims at removing near well bore impedances, enhancing the access to natural fractures and providing efficient fracture initiation points for hydraulic stimulation. Therewith, the developed technology has the potential to reduce the efforts of hydraulic stimulation and to increase the production rate of a well. The principles of this process are introduced and a process procedure is developed, which facilitates the application in deep bore holes. The operational readiness of the technology is shown in a field test conducted in the Grimsel Test Site. Two different enlargement geometries could be successfully drilling in a water-filled bore hole in a maximal depth of 13.8m. In summary, this thesis discusses the viability of thermal spallation drilling for deep drilling operations. Two major application possibilities are revealed: a combined thermo-mechanical drilling system for drilling deep wells in hard rock sections and thermal bore hole enlargement, to increase the diameter in the production zone of the well. For each of this two technologies a field test is conducted or prepared, demonstrating the operational readiness of the systems, which could be achieved during the progression of this project. Therewith, the thesis shows that thermal spallation drilling can contribute to the development of geothermal energy production from deep resources, as it can be used to enhance the drilling process and to increase the production rate.