Photon counting technology is available for decades, but it’s application in medical transmission imaging has only begun. One reason for the late adoption were pulse pileup effects at high X-ray flux which did not allow the usage of the technology in most clinical fields. But by using small detector elements and a low X-ray flux, the count rate in one pixel could be kept on an acceptable level to achieve sufficient image quality. Coincidentally, this met the requirements for one clinical application: breast imaging. The high spatial resolution, due to the small detector elements, allows the detection of microcalcifications while the low dose environment and the high dose efficiency made the detector an ideal candidate to be used in a screening system. Furthermore, due to the homogeneous composition of the breast, no large flux deviations are expected behind the object. Therefore, in 2003, the first photon-counting mammography system was introduced. Since mammography has its limitations, such as low sensitivity in dense breasts and low patient comfort, it remains reasonable to look for alternatives. In 2007, the first founding projects focused on a new modality, a photon-counting breast CT, were launched. The new device should offer at least the same performance as mammography at similar dose levels, as well as higher soft tissue contrast and higher patient comfort. Using simulations and measurements, a tube voltage of 60 kV with 3 mm Al filtration was found to be the optimum regarding dose reduction, soft tissue contrast, and possible spectral applications. Cadmium telluride (CdTe) was chosen as a sensor material due to its quality, availability, and detection efficiency. To attenuate almost 100 % of the X-rays at a tube voltage of 60 kV, the detector thickness was chosen to be 750 μm. A pixel pitch of 100 μm with a magnification of 1.3 results in a virtual pixel spacing of 76 μm in the rotation center, which is comparable to the pixel pitch in mammography (50–100 μm). The first breast CT demonstrators were ready in 2016, the product was launched in 2018, followed by the first clinical installation and the first patient scans in the same year. This made the breast CT the world’s first CT in clinical use equipped with a photon-counting detector. Expert opinions already confirmed that breast CT provides high quality images and is a viable alternative to mammography or tomosynthesis, especially in those patients reluctant to undergo mammography because of the issue of breast compression. Breast cancer detection rates have notably increased at the first sites, which are attributed primarily to the fact that women who had previously refused routine check-ups are now much more willing to undergo the examination due to the lack of breast compression. Also, a decrease in the number of recalls that would otherwise have been caused in mammography because of superimposed structures was observed. Currently, a clinical study is ongoing to prove the clinical performance of the modality. The aim of the study is to show that contrast-enhanced breast CT can replace a more expensive and time-consuming contrast-enhanced breast MRI examination. Future developments focus on the integration of a biopsy unit and the capability to utilize the spectral properties of the detector. By using k-edge imaging, the quantification of iodine and the calculation of virtual non-contrast images were already proven to be successful in phantom images. This can improve the diagnostic accuracy of functional imaging while reducing the patient dose by up to 50 % because a pre-contrast scan is no longer essential. By utilizing direct converting detector technology, breast CT integrates the strengths of mammography, tomosynthesis, and MRI technologies in one system. It is the only modality that allows for detection and assessment of microcalcifications due to fully 3D, high spatial resolution, and noninvasive differentiation of benign and malignant microcalcifications and lesions due to excellent soft tissue and functional imaging capabilities. With photon-counting breast CT, diagnostic and treatment care pathways of patients with breast disease can be enhanced.