Over the past two decades the nitrogen-vacancy (NV) center in diamond has been used to demonstrate and develop a variety of sensing protocols for static magnetic and electric fields, pressure, temperature, fluctuating fields, etc. Large corporations and start-ups are currently bringing NV sensors to the next technology-readiness level. However, it has also become apparent that such devices suffer from certain shortcomings, in particular for sensing at very high magnetic fields (>1 Tesla) and high stresses (> 100 GPa). These drawbacks could be overcome using group-IV-vacancy centers in diamond, in particular SiV, GeV, and SnV complexes. The goal of the project is the development of diamond-based quantum sensors for sensing at high magnetic fields and high stresses, which can be generally called “sensing at extreme conditions”. At the core of the project is the fabrication of shallow group-IV-vacancy centers with superior optical and spin coherence properties. Preliminary estimates demonstrate that, depending on exact experimental conditions, with appropriate defect engineering, coherence times could be increased by two orders of magnitude beyond what is currently achievable. Advances in engineering will be supported by theoretical work that will provide guidance and insights into the fundamental limits of optical and spin coherence times of group-IV-vacancy complexes. These centers will then be used to demonstrate two proof-of-concept sensing protocols beyond the limitations of NV-center-based technologies: (i) quantum magnetometry at Tesla-range magnetic fields; (ii) quantum sensing at stresses >100 GPa. For the latter, we aim at the measurement of the magnetic field, as well as the entire stress tensor and its distribution in the diamond crystal at “extreme” pressures. Along with the experimental demonstrations of these protocols, the work in the project will yield new knowledge about fundamental properties of point defects in extreme conditions, expanding the general knowledge of diamond as a quantum material. Fundamental aspects of defect physics will be investigated via a very close collaboration between theory and experiment.