Precise control of quantum effects is vital to the realization of entirely new technologies. For example, a computer based on quantum physical principles is expected to outperform today's classical computers. In communication technology, quantum devices are already commercially available which allow secure transmission of data. Controlling the properties of photons down to the quantum level is at the heart of these technologies. In recent years, scientists in the group of Prof. Gerhard Rempe, Director at the Max Planck Institute of Quantum Optics (MPQ) in Garching, have managed to control the shape, frequency and polarization of single photons. However, only now have they been able to also tune the phase of single photons, as they report in Nature Photonics (Advanced Online Publication, DOI: 10.1038 /NPHOTON.2009.115, 13 July 2009). While offering new applications in quantum information technologies, these results are also of fundamental importance for understanding the quantum behavior of light.