Similar to the quantization of electrical conductance, there is a quantization of thermal conductivity if the dimensions of the objects of investigation are reduced to the atomic scale. With our self-developed, high-resolution, sub-micron-sized heat transfer sensors, we are able to precisely measure the heat transfer through single atomic junctions. These measurements are performed using the break junction method: first, a reliable contact across many atoms is established between the sample and the tip of a scanning tunneling microscope. This contact can be verified by measuring the electrical resistance. From this position, the tip is retracted from the sample with picometer precision while observing the breaking of individual atomic junctions, until only one junction remains to be investigated. Since a sub-micron-sized heat transfer sensor is embedded in our tips, we can now perform heat transfer measurements through this atomic junction. This allows for an investigation of the validity of the Wiedemann-Franz Law, known from bulk metals, at the atomic scale. This quantized thermal conductance of different materials is another, newer topic of research in our group.