Layer-thickness measurement is one of the most promising and attractive fields of application for terahertz measurement systems, as they really provide benefits in comparison to competing techniques. In contrast to ultrasound systems, terahertz measurements can be carried out without a coupling medium and is therefore a truly contactless measurement. The possibility to measure individual layers in a multilayer stack is highly advantageous in contrast to established eddy current measurement devices. Unlike X-ray devices, terahertz radiation of common measurement systems is not harmful to biological tissue. Terahertz measurement systems have undergone a remarkable development in terms of the performance as well as in the evaluation algorithms. Increase of speed and enhancement of measurement robustness make these optically complex systems ready for industrial employment. In our contribution, we will cover the development of photonic terahertz measurement systems with a focus on terahertz layer thickness determination.